The  Topography  of  the  Chlorophyll  Apparatus 
in  Desert  Plants. 


BY 


WILLIAM  AUSTIN  CANNON. 


•he  Induction,  Development,  and  Heritability 
of  Fasciations. 


BY 


ALICE  ADELAIDE  KNOX. 


QK882 
C3 


WASHINGTON,  D.  C. 

Published  by  the  Carnegie  Institution  of  Washington. 

1908. 


ulljp  i.  B.  'Ml  iCtbrarg 

1                                            ^rC 

1                          /<^.' 

ffi^ 

C3 

a  State  Library 


Gift  of 


The  Topography  of  the  Chlorophyll  Apparatus 
in  Desert  Plants. 


BY 


WILLIAM  AUSTIN  CANNON, 


The  Induction,  De\elopment,  and  Heritability 
of  Fasciations. 


BY 


ALICE  ADELAIDT^   t-x-r^v 


THIS  BOOK  IS  DUE  ON  THE  DATE 
INDICATED  BELOW  AND  IS  SUB- 
JECT  TO  AN  OVERDUE  FINE  AS 
POSTED  AT  THE  CIRCULATION 
DESK. 


WASHINGTOli 

Published  i-.y  the  Carnegie  Ins! 

I  908.  I 


f^t  H.  Hilt 


ft.'^ 


iooM/5-79 


o    O   V.  '— ' 


CARNEGIE  INSTITUTION  OF  WASHINGTON 
Publication  No.  98 


THE  CORNMAN   PRINTIXG  CO. 
C'ARI^ISLE,   PA. 


The  Topography  of  the  Chlorophyll  Apparatus 
in  Desert  Plants. 


BY 


WILLIAM  AUSTIN  CANNON. 


Cannon 


\  f 


A  — KRAMERIA  CANESCENS.  Branch  from  a  plant  which  is  growing  on  the  slope 
at  the  northern  base  of  the  Tumamoc  Hill.  This  is  a  plant  with  the  deciduous 
habit.     April  25,   1907. 

B._COVILLEA  TRIDENTATA.  Branch  in  fruit  of  a  plant  which  is  growing  near  the 
laboratory  building.     This  is  an  evergreen.     April  25,    1907. 


THE  TOPOGRAPHY  OF  THE  CHLOROPYHLL  APPARATUS 
IN  DESERT  PLANTS. 


ENVIRONMENTAL  CONDITIONS  IN  RELATION  TO  STRUCTURE. 

The  plants  which  come  under  observation  in  this  paper  are  fairly  repre- 
sentative of  the  perennials  of  the  Tucson  region  (2000  to  3000  feet),  with 
an  average  rainfall  of  12  inches,  and  occur  in  a  comparatively  wide  range 
of  habitats.  These  include  the  bottom-lands  of  the  Santa  Cruz  River  which 
are  bordering  upon  the  Laboratorv  domain;  low  desert  mountains,  Tumamoc 
Hill  (a  portion  of  the  Laboratory  domain);  the  lower  slopes  and  washes  of 
Tumamoc  Hill ;  dry,  low  ridges,  the  so-called  aerial  mountain-deltas,  which 
lead  eastward  from  the  main  range  of  the  Tucson  Mountains;  the  broad 
and  gently  rolling  mesa  or  table-land;  and,  finally,  the  bed  of  the  Santa 
Cniz  River  and  certain  contiguous  irrigating  channels  and  roadside  ditches. 

In  these  habitats  a  relatively  large  range  of  environmental  conditions  are 
encountered.  In  them  there  is  a  wide  variety  of  soils,  of  drainage  condi- 
tions, and  of  exposure  to  light  and  to  air-currents.  The  bottom-lands  are 
characteristically  deep  and  are  made  up  largely  of  a  clay  or  loam,  with 
strata  of  sand  some  distance  beneath  the  surface.  Toward  the  sides  of  the 
bottom-lands  the  top-soil  becomes  more  or  less  sandy  or  gravelly,  with  the 
coarser  material  on  the  slopes  immediately  above  and  leading  out  of  the 
bottoms.  Then  comes  either  the  mesa  with  its  thin  layer  of  top-soil  and  a 
nearly  impervious  hardpan  underlying  it,  or  the  lower  slopes  of  the  desert 
mountains,  with  coarse  rock  and  bowlders  and  bed-rock,  clayish  soil,  more 
perfect  drainage,  and  various  exposures. 

The  water-table  of  the  river-bottom  lies  from  6  to  12  m.  from  the  surface 
of  the  soil;  that  of  the  mesa  is  frequently  25  m.  and  deeper  beneath  the 
surface.  The  location  of  the  reservoirs  of  water  on  the  mountain  have  not 
been  determined,  but  are  possibly  connected  with  the  fissures  and  the 
pockets  in  the  rocks. 

Very  curiously  the  leaf-habit  of  these  desert  forms,  and  even  their  general 
xerophytic  character,  are  not  consistently  associated  with  the  character  of 
the  habitat.  This  will  be  apparent  from  a  few  examples.  The  evergreen 
habit  is  not  correlated  with  the  conditions  of  water-supply,  or  at  least  with 
the  only  sure  water-supply — that  of  the  river-bottoms.  Of  the  plants  studied 
in  connection  with  this  paper  which  do  not  drop  their  leaves  with  change  of 

3 


4  TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IX  DESERT  PLANTS. 

seasons,  Covillca  tridcntata  (plate  1,  b)  and  CcUis  pallida  (plate  2,b),  the 
former  stows  on  the  mesa  and  the  latter  on  the  slopes  of  the  mountain. 
Also  what  is  outwardly  and  palpably  the  most  extreme  type  of  xerophyte, 
Kirbcrlinia  spinosa  (plate  3,  a)  having  leaves  only  when  in  the  seedling- 
stage,  which  is  provided  with  palisade  chlorenchyma,  a  very  heav\'  epider- 
mis, and  with  deeply  sunken  stomata,  appears  most  frequently,  perhaps,  in 
places  where  the  soil  is  quite  deep.  In  other  words,  this  form  avoids  the 
driest  situations.  Other  forms  which  are  leafless  in  dry  times  and  there- 
fore the  most  of  the  year,  as  Baccharis  emoryi  (and  perhaps  Aster  spinosus 
should  be  included,  although  it  has  annual  subaerial  parts),  and  have  xero- 
phytic  structure,  are  to  be  found  only  along  the  river-beds  or  where  the  water 
conditions  are  most  favorable.  Cacti,  however,  are  usually  found  in  dry  sit- 
uations .  This  is  probably  associated  with  their  habit  of  treasuring  the  scant 
amount  of  water  as  it  comes  to  them  from  the  rains,  in  place  of  depending 
on  subirrigation,  as  in  the  other  forms  given.  Prosopis,  which  has  a  con- 
stant as  well  as  abundant  water-supply,  forms  and  sheds  its  leaves  with  the 
advent  and  passing  of  the  seasons  in  a  manner  usually  and  perhaps  always 
quite  independent  of  the  time  or  the  amount  of  the  rainfall.  Certain  of  the 
more  gross  characters  of  these  desert  plants  are  thus  scarcely  to  be  attrib- 
uted to  the  molding  influences  of  the  environment;  it  will  doubtless  be 
necessary  to  take  into  consideration  the  peculiar  history  of  each  plant,  its 
gradual  modification  from  its  remote  mesophytic  ancestor,  before  habits 
and  structure  are  satisfactorily  related. 

As  is  well  known,  a  leading  feature  of  the  morphology  of  desert  perenni- 
als is  the  reduction  of  the  transpiring  surface.  Plants  may  be  wholly  with- 
out leaves,  or  leaves  may  be  present  during  early  growth  or  during  favor- 
able seasons  only,  or  if  leaves  are  a  feature  they  may  be  much  reduced  in 
size  (plate  4).  In  the  former  instances  the  twigs  and  the  branches  assume 
the  functions  of  leaves;  in  the  last  case  it  will  be  shown  in  this  paper  that 
the  same  is  also  true  when  leaves  are  present  but  reduced  in  size  or  present 
during  favoring  seasons  only. 

Among  other  characters  which  distinguish  the  leaves  of  xerophytes  is  the 
palisade  nature  of  at  least  the  subepidermal  portion  of  the  chlorenchyma. 
That  is,  the  chlorophyll  tissues  of  the  leaf  are  to  a  greater  or  less  extent 
composed  of  cells  whose  long  axes  are  placed  at  right  angles  to  the  surface 
of  the  leaf.  It  is  of  interest,  therefore,  to  learn  how  far  the  structure 
characteristic  of  the  leaves  is  found  in  such  stems  as  exercise  the  function 
of  leaves. 

To  anticipate  one  of  the  findings  of  this  paper,  in  plants  whose  transpiring 
surface  is  most  perfectly  reduced  the  chlorenchyma  of  the  stem  is  in  certain 
regards  very  like  that  in  the  leaf  of  the  same  species ;  but  in  those  with  a 
more  or  less  pronounced  leaf-surface  the  chlorenchyma  of  the  stem  is  unlike 
that  of  the  leaf.     In  the  former  case  the  stem  structure  is  palisade;   in  the 


ENVIRONMENTAL    CONDITIONS    IN    RELATION    TO    STRUCTURE.  5 

latter  it  is  spon.o-y.  The  immediate  reason  for  this  variation  is  not  clear. 
The  environmental  conditions  of  the  two  classes  of  plants  may  be,  as  far 
as  one  can  determine,  quite  the  same.  The  cause  of  this  must  evidently 
be  looked  for  elsewhere  and,  as  will  be  shown  below,  may  perhaps  be  asso- 
ciated with  the  character  of  the  structures  exterior  to  the  chlorenchyma. 

A  noticeable  feature  of  many  of  the  desert  plants  as  opposed  to  those  of 
the  humid  regfions— a  feature  very  conceivably  related  to  the  distribution  of 
chlorophyll  in  the  stems— is  the  open  character  or,  in  a  measure,  the  loose- 
ness of  growth.  This  is  characteristic  of  both  trees  and  shrubs.  Among- 
the  shrubs  this  appearance  is  due  in  part  to  the  relatively  small  number  of 
branches  and  in  part  to  the  small  size  of  the  leaves.  Quite  likely  the  latter 
is  the  leading-  reason  in  either  trees  or  shrubs.  As  a  result,  all  portions  of 
the  plant  are  exposed  either  to  direct  sunlig-ht  or  to  very  strong-  illumination 
at  all  times  during-  the  day.  The  light  conditions  are  such  in  consequence 
that  wherever  chlorophyll  is  to  be  found,  even  in  the  oldest  parts,  as  it  is 
in  Parkinsonian  photosynthesis  can  take  place. 

On  the  other  hand,  the  various  positions  attained  by  the  branches  as 
related  to  the  incident  rays  of  lig-ht  insure  a  certain  degree  of  protection 
from  the  most  intense  lig-ht,  as  is  found  in  such  plants  as  Smi/ax,  of  the 
Florida  scrubs,  for  example,  by  the  erect  posture  of  the  leaves. 

In  considering-  the  affinities  of  the  plants  which  have  been  under  obser- 
vation and  their  distribution,  it  is  of  interest  to  note  that  their  nearest 
relatives  are  desert  forms .  As  one  result  of  this  fact,  the  possibility  of  com- 
paring- congeners  growing-  in  desert  and  in  humid  regions  is  in  many  cases 
precluded  and  one  important  source  of  evidence  as  to  the  direct  origin  of 
these  plants  is  thrown  out.  Those  plants  which  are  confined  to  North  or 
South  America  include  Bacc/mris,  Ccreus,  Condalia,  Covillea,  Franseria, 
Krameria,  Fouquieria,  Ka^berlinia,  and  Olneya,  which  occur  in  the  arid 
regions  of  North  America  only.  Ephedra,  Prosopis,  and  Zizyphus  have 
nearly  worldwide  distribution,  since  they  occur  both  in  the  Old  and  the  New 
Worlds  and  in  both  hemispheres,  but  not  in  colder  regions.  Celtis  is  the 
only  marked  exception  and  has  representatives  in  cold  temperate  and 
humid  regions,  as  well  as  in  the  warm  and  dry  regions,  and  is  practically 
cosmopolitan  in  distribution. 


O  TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IN  DESERT  PLANTS. 

SCOPE  AND  PURPOSE. 

Field-studies  on  the  transpiration  of  desert  plants  when  in  a  leafless  con- 
dition, either  as  a  result  of  the  usual  seasonal  changes,  the  advent  of 
drous'ht,  or  normally  without  leaves,  lead  to  the  discovery  that  with  deli- 
cate apparatus*  the  evolution  of  watery  vapor  can  be  demonstrated  when 
it  might  be  least  expected  and  in  surprisingly  large  amounts.  Some  of  the 
plants  thus  studied  were  Cereiisgiganteus,  Echuwcadus  wislizcni ,  Fouqiiieria 
splendejis,  Kccberlinia  spinosa,  Opuntia  versicolor,  Parkinsonia  viicrophylla, 
and  others. t  This  work  early  suggested  an  examination  into  the  extent  of 
chloro]:)hyll  and  the  character  of  the  chlorophyll-bearing  tissues  in  the  con- 
stant parts  of  the  plants.  As  opportunity  offered  the  work  was  carried  on, 
and  it  demonstrated  so  much  of  interest  that  a  summary  was  presented  before 
the  Botanical  Society  of  America,  New  Orleans,  December,  1905. 

Any  satisfactory  study  of  the  chlorophyll  relations  of  the  desert  plants 
must  take  into  account  the  peculiar  light  conditions  to  w^hich  the_\-  are  ever 
exposed.  In  the  present  study  no  attempt  has  been  made  to  do  this,  in  part 
because  of  the  complexity  of  the  subject,  in  part  because  of  the  lack  of  sat- 
isfactory instiiiments  for  making  light  measurements.  It  therefore  has 
been  limited  to  an  observation  of  the  chlorophyll  apparatus  as  it  exists, 
without  reference  to  correlations  other  than  the  obvious  biological  ones 
which  cropped  up  everywhere  throughout  the  entire  course  of  the  work. 

METHODS  AND  MATERIAL. 

In  such  a  research  as  the  present  one  living  material  at  hand  is  a  prime 
necessity,  for  the  reasons,  which  are  very  obvious,  that  chlorophyll  can  be 
most  satisfactorily  identified  in  living  material,  and,  furthermore,  a  large 
quantity  of  material  is  a  necessity  from  wdiich  to  select  what  is  representa- 
tive as  well  as  by  which  to  know  the  range  in  variation  of  the  structures  to 
be  studied. 

While  unusual  conditions  have  been  taken  into  account,  this  paper  aims  to 
present  ])rimarily  the  usual  and  normal  condition  of  the  chlorophyll  ap])a- 
ratus.  In  every  instance  conclusions  were  drawn  from  the  study  of  only 
normal  and  healthy  plants,  and  with  but  one  exception  {Parkinsonia  acu- 
leatd)  the  plants  were  studied  in  their  proper  habitats. 

The  developmental  method  of  study  was  employed.  That  is  to  say,  vig- 
orous branches  or  stems  were  selected  and  sections  were  made  at  measured 
intervals  from  the  tip.  Whenever  necessary,  comparative  observations,  in 
addition,  were  made  on  mature  structures,  so  that  in  each  instance  the  story 
might  be  as  complete  as  possible.     The  presence  of  chlorophyll  in  a  stem 


*Cannon,  W.  A.:  A  new  method  of  measuring  the  transpiration  of  plants  in  place. 
Bull.  Torn  Bot.  Club,  1905,  32  :  515. 

tCannon,  W.  A.:  On  the  transpiration  of  Fouquierias  plendens,  Bull.  Torr.  Bot. 
Club,  1905,  32:397;  and  Biological  relations  of  certain  Cacti,  The  American  Naturalist, 
1906,  40 :  27. 


SPECIAL   part:     the   CHLOROPHYLL   APPARATUS. 


was  determined  by  inspection  onl3%  and  all  chloroplastids  that  from  com- 
parison were  seen  to  be  normally  colored  were  classed  as  being-  functional 
and  were  considered  as  having-  adequate  amounts  of  light  and  of  air. 

The  following-  plants  were  passed  imder  observation  during  the  course  of 
this  study:  Aster  spinosns  Benth.;  Baccharis  emoryi  Gray;  Celtis  pallida 
Torr.;  Cernis gigantcus  Englm.;  Condalia  spatJmlaca  Gray;  Covillea  tridentata 
Vail;  Ephedra  antisyphilitica  C.  A.  Meyer;  Foiiqideria  splendens  Englm.; 
Franseria  djdnosa  Gray;  Ka^berlinia  spinosa  Zucc;  Kramer ia  caiiescens  Gray; 
Olneya  tesota  Gray;  ParJcinsoiiia  aadeata  L.;  Parkinsoniainicrophylla  Torr.; 
Parkinsonia  torreyana  Watson;  Prosopis  velutina  Wooton;  Salix  nigra  Marsh. ; 
SaDibucits  mcxicana  Presl.;  Zizyp/nis  parry i  Tow. 

SPECIAL  PART:     THE  CHLOROPHYLL  APPARATUS. 

Aster  spinosus;  Baccharis  emoryi.  (Fig.  i.) 
These  plants  inhabit  the  wash  along-  the  river  and  the  irrigating-  and 
wayside  ditches,  where  water  is  frequently  to  be  found.  Aster  spinosus  is 
an  annual  with  perennial  root;  Baccharis  emoryi  is  perennial.  Both  Aster 
and  Baccharis  are  usually  devoid  of  leaves,  but  the  young-  portions  at  least 
are  supplied  with  rudimentary  ones. 


Fig.  I. — Baccharis  emoryi:  A.,  segment  from  transverse  section  of  young 
stem  to  show  the  character  of  cortical  chlorophyll  band  {ch.  b.) ;  i>',  sec- 
tion of  leaf,  magnified  as  in  A."^ 

Chlorophyll  of  the  stem  is  confined  to  the  cortex  in  both  species  and  in 
both  the  chlorenchyma  is  palisade.  The  palisade  in  the  stems  of  each  also 
closely  resembles  that  in  the  rudimentary  leaves  of  the  same  species.  This 
similarity  in  the  structure  of  the  chlorophyll  band*  in  the  stem  and  of  the 

*In  all  figures  chlorophyll  is  indicated  by  stippling. 


TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IN  DESERT  PLANTS. 


chlorenchyma  of  the  leaf  was  observed  also  in  Kramcria  cancsccns,  where 
the  cortical  chlorophyll  band  is  likewise  palisade. 

Celtis  pallida.    (Plate  2,  u,  and  figs.  2  and  3.) 

The  si:)ccimen  of  Celtis  which  was  chosen  for  study  is  .qrowin.y-  in  the 

arroyo  below  and  to  the  east  of  the  Laboratory  bnildin.q-.     A  branch  about 

2  m.  in  lenofth  was  selected  and  sections  made  at  the  followinq-  distances 

from  the  tip:     6,  21,  34,  49,  64,  79,  144,  and  178  cm.     The  parts  of  the 

branch  where  the  sec- 
tions were  made  had 
the  following-  diame- 
ters: 2,  3.5,4,  4.5,  6, 
8,  8.5  mm.  and  1  and 
1.6  cm.,  respectively. 
A  section  of  a  branch 
2  mm.  in  diameter  and 
6  cm.  from  the  tip 
shows  the  following- 
ijeneral  structiiral  re- 
lations : 

Cortex:  There  are 
several  well  -  defined 
cortical  divisions.  An 
epidermis  with  a  thin 
outer  wall  and  a  sub- 
epidermal tissue  about 
three  cells  in  thick- 
ness bound  the  stem. 
Within  this  lies  a 
c  h  1  o  r  o  p  h  }•  1 1  band 
which  is  also  about 
three  cells  in  thick- 
ness. A  discontinuous  ring  of  hard  bast  is  situated  within  the  chlorophyll 
band.  Between  the  hard  bast  and  the  cambium  is  the  region  of  the  inner 
cortical  parenchyma. 

Woody  cylinder:  The  wood  is  composed  very  larg-ely  of  wood  fibers  with 
a  noticeably  small  amount  of  wood  parenchyma.  The  pith  is  well  marked 
but  does  not  need  further  mention  in  this  connection. 

Chlorophyll  occurs  in  the  outer  cortical  parenchyma,  in  much  of  the  par- 
enchyma which  lies  between  the  hard  bast  and  the  wood,  in  the  medullar\- 
rays,  both  of  wood  and  of  cortex,  and  in  the  outer  cells  of  the  pith. 

*  The  term  chlorophyll  band  as  used  in  this  paper  refers  to  that  portion  of  the  cortical 
parenchyma  tliat  lies  between  the  epidermis  and  the  ring  of  mechanical  tissue  which  is 
about  midway  lietween  the  epidermis  and  the  cambium.  It  is  the  largest  and  the  most 
enduring  chlorophyll  tissue  in  the  stem. 


Fig.  2.— Celtis  pallida:  A,  section  of  branch  2  mm.  in  diam- 
eter; B,  section  of  branch  3.5  mm.  in  diameter. 


Cannon 


Plate  2 


A^  „ 


W'^lh- 


;"^-:<: 


A.— CONDALIA  SPATHULACA.  Branch  from  a  plant,  which  is  an  evergreen,  grow- 
ing on  the  rocks  below  and  to  the  north  of  the  laboratory  building.    April  25,  1  907  . 

B.— CELTIS  PALLIDA.  Portion  of  a  branch  from  a  plant  which  is  growing  near  the 
Condalia  of  "A,"  showing  the  character  of  the  leaf-covering.  This  also  is  an  ever- 
green. 


CELTIS    PALLIDA. 


With  an  increase  in  diameter  of  the  stem  characteristic  changes  take  place, 
more  particularly  in  the  cortex,  which  greatly  affect  the  topography  of  the 
chlorophyll  apparatus.  As  the  cortex  becomes  wider,  ring's  of  secondary 
hard  bast  are  formed  within  the  i^rimary  ring-;  parenchyma,  which  for  the 
most  part  contains  chlorophyll,  extends  between  these  ring-s.  The  groups 
of  bast  are  connected  in  part  or  always  by  medullary  rays.  As  the  stem 
increases  in  diameter  these  groups  are  pushed  farther  and  farther  apart 
and  the  intervening-  portion  becomes  filled  with  parenchyma  which  contains 
chlorophyll.  In  this  respect  Celtis  striking-ly  resembles  Prosopis.  The  sec- 
ondary hard  bast  of  the  former,  however,  is  not  placed  as  regularly  as  in 
Prosopis,  and  the  chloroi:)hyll  distribution,  consequently,  of  Celtis  is  not  so 
symmetrical  as  in  the  other  species. 


Fig.  t,.— Celtis  pallida:  A,  section  of  branch  4.5  mm.  in  diameter;  B,  detail  of  A. 
showing  presence  of  chlorophyll  in  secondary  cortex;  caw.,  cambium;  cli.b.,  cortical 
band  of  chlorophyll;  h.  b.,  hard  bast;  )ued.,  medullary  ray;/^//.,  phellogen;^//.  d, 
phelloderm. 

But  the  greatest  change  in  the  chlorophyll  apparatus  occurs  as  a  result 
of  the  formation  of  phelloderm.  The  cork-cambium  arises  in  the  cells  imme- 
diately outside  the  chlorophyll  band  and  by  its  activity  gives  rise  to  periderm 
without  and  phelloderm  within.  The  latter  contains  chlorophyll.  When 
the  amount  of  phelloderm  about  equals  the  thickness  of  the  chlorophjdl 
band  no  more  appears  to  be  formed.  The  result  is  that  the  chlorophyll 
band  of  stems  from  4  mm.  to  1.6  cin.  in  diameter  is  about  half  phelloderm. 
How  this  relation  is  in  older  stems  was  not  learned. 

How  long  the  chlorophyll  remains  active  in  the  stem  was  not  determined. 
It  is  present  in  the  outer  portions  of  the  pith  in  the  stems  8.5  mm.  diaineter 
after  it  has  disappeared  from  the  medullary  rays,  but  whether  this  is  a  con- 


10 


TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IN  DESERT  PLANTS. 


stant  relation  was  not  learned.      In  a  branch  1.6  cm.  in  diameter,  as  well 
as  one  1  cm.  in  diameter,  the  chlorophyll  was  confined  to  the  cortex. 
The  following:  measurements  were  made: 


Distance 
of  section 
from  tip. 

Diameter        Width  of 
of  stem.            cortex. 

Depth  of 
phelioderm. 

Width  of 
phelioderm. 

Depth  of 

chlorophyll 

band. 

Width  Of 

chloropliyll 

band. 

cm. 
6 

21 

34 

64 
79 

vim. 

2 

3-5 
4 

8 
10 
16 

320 
300 

547-8 
547.8 
581 
1079 

80 
76.8 
80 
118. 4 

39-2 

22.4 

32 

19.2 

28 

28.8 

M 

78 

96 

89.6 
102.4 
102 

96 
108.8 
147-2 

M 

41.6 
25.6 
2S.S 

22.4 
32 

35-2 
25.6 
32 

CoNDALiA  SPATHULACA.     (Plate  2,  A,  and  fig.  4.) 

The  plant  from  which  the  branch  studied  was  taken  is  g-rowin.q-  by  the 
Hospital  Road  near  the  northeast  corner  of  the  Laboratory  domain.  The 
shiiib  is  about  1.5  m.  high  and  is  a  very  vig-orous  one. 

vSections  were  made  at  the  fol- 
lowing- distances  from  the  tip: 
2,  5,  20,  35,  65,  95  cm.  These 
were  1.5,  2,  4,  7.5  mm.  and  1.2, 
1.7  cm.  in  diameter,  respec- 
tively. 

A  cross-section  of  a  young 
branch  1.5  mm.  in  diameter  and 
2  cm.  from  the  tip  shows  the 
following  leading  structural 
characters:  An  epidermis  with  a 
thin  cuticle  bounds  the  stem. 
Within  this  is  a  hypodermal  por- 
tion three  cells  thick,  and  within 
this,  again,  is  a  collenchyma-like 
tissue  about  as  thick.  The 
chlorophyll  band,  about  three 
cells  wide,  lies  immediately  within  the  last-mentioned  tissue  and  occupies 
the  central  portion  of  the  cortex.  A  relatively  narrow  inner  cortical  portion 
separates  the  chlorophyll  band  from  the  cambium.  This  inner  part  consists 
of  a  discontinuous  hard-bast  ring  and  thin- walled  parenchyma .  The  former 
abuts  on  the  chlorenchyma.  The  wood  and  the  pith  present  no  character- 
istics of  interest  in  the  present  connection.  In  addition  to  the  chlorophyll 
band,  chlorophyll  occurs  also  in  most  of  the  inner  cortical  parenchyma,  in 
the  medullary  rays  of  the  wood,  and  in  the  outer  pith-cells. 


Fig. 


4. — Condalia  spathulaca:  Section  from 
a  branch  2  mm.  in  diameter. 


CONDALIA    SPATHULACA. 


11 


The  chlorophyll  band  is  a  relatively  naiTow  tissue  which  lies  rather  deeph^ 
in  young:  stems,  but  in  older  ones  much  nearer  the  surface  (see  table 
of  measurements  below) .  The  cells  are  either  cuboid  or  slig-htly  elon^-ated. 
If  the  latter  the  long-  axis  is  tangential  to  the  surface. 

AVith  increase  in  diameter  certain  changes  take  place  in  the  stem  which 
are  most  marked  in  the  cortex.  Cork  is  formed  in  very  small  stems.  In 
a  stem  2  mm.  in  diameter  and  5  cm.  from  the  tip  it  was  observed  in  the 
hypodermal  cells,  where  a  considerable  amount  of  periderm  was  organized. 
This  is  more  pronounced  in  branches  4  mm.  and  still  more  in  those  7.5  mm. 
in  diameter.  The  phelloderm,  however,  is  not  formed  until  the  stem  is 
somewhat  older.  In  a  stem  1.2  cm.  in  diameter  the  phelloderm  was  about 
two  cells  in  thickness  and  was  chlorophyll-bearing;  in  a  branch  1.7  cm.  in 
diameter  the  amount  of  chlorophyll-bearing-  phelloderm  was  so  great  as  to 
considerably  increase  the  width  of  the  chlorophyll  tissues.  The  chlorophyll 
early  leaves  the  wood  and  the  pith;  in  a  stem  only  7.5  mm.  in  diameter  it 
was  confined  to  the  outer  portion  of  the  cortex. 

The  following  measurements  were  made: 


Diameter 
of  branch. 

Distance 
from  tip. 

Width  of 
cortex. 

Width  of 
chloropliyll 
1,       band. 

Depth  of 

chlorophyll 

band. 

mm. 

cm. 

M 

!    - 

M 

1-5 

2 

208 

38.4 

70 

2 

5 

256 

i   32 

80 

4 

20 

448.2 

25.6 

64 

7-5 

35 

1162 

64 

64 

12 

65 

1494 

80 

19.2 

17 

95 

1147 

73-6 

41.6 

COVILLEA  TRIDENTATA.     (Plate  I,  B,  and  fig.  5. 


The  plant  from  which  the  branch  stitdied  was  taken  is  growing  near  the 
road  a  few  meters  east  of  the  Laboratory  building.  Sections  were  cut  at 
the  following  distances  from  the  tip:  5,  10,  20,  35,  65,  95  cm.,  and  were 
1,  1.5,  3,  4.5,  7.5,  9.5  mm.,  respectively,  in  diameter. 

The  young  and  angular  stem,  1  mm.  in  diameter,  has  the  following  gen- 
eral relations  of  its  tissues:  Within  the  epidermis,  which  has  a  rather  thin 
cuticle,  lies  the  broad  chlorophyll  band,  which  is  about  three  cells  in  thick- 
ness. A  discontinuous  hard-bast  ring-  is  placed  immediately  within  the 
chlorophyll  band.  This  is  made  up  of  larger  and  of  smaller  groups,  of  which 
the  former  lies  opposite  the  angles  of  the  stem.  More  or  less  stony  tissue 
also  is  found  in  the  same  ring.  Between  the  groups  of  mechanical  tissue 
is  thin- walled  parenchyma.  Within  the  hard-bast  ring,  and  separating  it 
from  the  cambium,  are  the  distal  ends  of  the  medullary  rays  and  paren- 
chyma between  them.  There  is  nothing  noteworthy  in  the  present  connec- 
tion regarding  either  pith  or  wood. 


12 


TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IN  DESERT  PLANTS. 


The  chlorophyll  band  is  made  up  of  cuboid  and  elongated  cells,  of  which 
the  latter  have  the  long:  axis  placed  parallel  to  the  surface  of  the  stem.  In 
addition  to  the  outer  chlorophyll  band,  chlorophyll  is  found  sparingly  in 
the  medullary  rays  both  of  the  cortex  and  of  the  wood  and  in  the  pith  also. 

With  increase  in  diameter  the  stem  exhibits  certain  changes  in  its  general 
structure,  of  which  the  most  important  in  the  present  connection  are  to  be 
found  in  the  cortex.  Cork  is  org-anized  early  and  is  superficial.  The 
phelloderm  is  in  direct  contact  with  the  chlorophyll  band  and  probably  con- 
tributes chloroi)hyll-bearing  cells  to  the  latter,  although  this  was  not 
definitely  determined.  The  other  changes  in  the  cortex  do  not  affect  the 
distribution  of  the  chlorophyll  and  may  be  neglected. 


Fig.  5. — Covillea  tridentata:  A,  transverse  section  of  stem  5  mm.  in  diam- 
eter, showing  character  of  spongy  tissue  of  chlorophyll  band;  i?,  transverse 
section  of  leaf,  showing  palisade  character  of  subepidermal  chlorenchyma; 
C,  cross-section  of  stem  i  mm.  in  diameter,  to  show  general  distribution  of 
chlorophyll.     Lettered  as  in  fig.  3. 

The  order  of  disappearance  of  chlorophyll  from  the  stem  was  not  followed. 
In  a  stem  1.5  mm.  in  diameter  chlorophyll  was  observed  in  the  pith,  in  the 
medullary  rays  of  wood  and  of  cortex,  and  in  the  chlorophyll  band.  In  a 
stem  3  mm.  in  diameter,  however,  it  had  practically  disappeared  from  all 
tissues  deeper  in  the  stem  than  the  chlorophyll  band;  in  a  stem  9.5  mm.  in 
diameter  no  traces  of  chlorophyll  were  to  be  detected  outside  of  this  band. 
No  chlorophyll  was  found  in  another  branch  2  cm.  in  diameter  and  145  cm. 
from  the  tip,  although  the  i:»rimitivc  chloroph\-ll  band,  but  without  chloro- 
phyll, was  .still  present. 


COVILLEA   TRIDENT  ATA. 

The  followino:  measurements  were  made: 


13 


Diameter 
of  branch. 

Distance 
from  tip. 

Width  of 
cortex. 

Width  of 

chlorophyll 

band. 

1 
Depth  of 
chlorophyll 
band. 

mm. 

cm. 

M 

M 

M 

I 

5 

.76 

48 

16 

1-5 

lO 

256 

118 

19.2 

3 

20 

332 

64 

48 

4-5 

35 

421 

80 

80 

7-5 

65 

421.6 

64 

32 

9-5 

95 

664 

64 

80 

Ephedra  antisyphilitica.     (Fig.  6.) 

Ephedra  occurs  in  the  wash  at  the  foot  of  Tumamoc  Hill,  to  the  west  of 
the  LaboratorJ^  The  specimen  selected  for  observation  forms  a  dense  shrub 
about  2  m.  hig-h,  which  has  found  refuge  from  predatory  cattle  by  growing- 
under  a  large  Acacia  greggii.  As  is  well  known,  the  plant  has  an  appear- 
ance much  like  that  of  scouring  rush,  which  is  due  to  the  numerous  slender 
branches  that  are  divided  into  sections  of  about  50  cm.  each.  These 
branches  are  the  only  green  ones  on  the  plant;  the  older  ones  are  covered 
with  a  rough  bark,  which  is  of  gray  color. 

The  oreneral  structure  of  one  of  the  green  branches  may  be  outlined  as 
follows:  An  epidermis  with  heavy  cuticle  and  with  deeply  sunken  stomata 
bound  the  stem.  The  stomata  are  regularly  disposed  in  a  manner  depend- 
ing on  the  arrangement  of  certain  mechanical  tissues  within  the  cortex. 
I  refer  to  bundles  of  fibers  which  occur  at  intervals  of  about  50  /*  on  the  inner 
edge  and  abutting  on  the  epidermis.  Between  the  bundles  the  surface  of  the 
stem  is  somewhat  depressed  and  in  these  channels  the  stomata  are  placed. 
The  cortex  is  composed  mainly  of  palisade  cells  which  are  chlorophyllaceous, 
but  fibers  in  groups  are  scattered  in  an  irregfular  fashion  through  the  cortex. 
The  wood  and  the  pith  in  young  stems  do  not  contain  chlorophyll;  in  older 
stems,  however,  the  medullary  rays  of  the  wood  are  supplied  with  chloro- 
phyll. 

The  younger  portions  of  the  green  branches,  with  a  diameter  of  1  mm., 
have  chlorophyll  in  the  cortex  only  and,  as  mentioned  above,  this  is  pali- 
sade. The  cells  range  in  length  from  15  i^^  to  65  /*,  and  of  these  the  shorter 
are  uniformly  near  the  woody  cylinder.  In  stems  1.5  mm.  in  diameter  the 
inner  cells  have  lost  their  palisade  character  and  are  more  or  less  cuboid. 
This  is  probably  owing  to  the  growth  in  diameter  of  the  stem  and  to  the 
consequent  tangential  stretching-  and  radial  compression  of  the  cortex. 
Finally,  these  inner  cells  become  elongated  in  a  direction  parallel  to  the 
surface,  so  that  their  primitive  character  is  wholly  lost. 

In  stems  2  mm.  in  diameter  the  diameter  of  the  woody  cylinder  and  the 
thickness  of  the  cortex  are  noticeably  increased  as  a  result  of  the  activity 
of  the  cambium.     The  topography  of  the  chlorophyll  apparatus  is  likewise 


14         TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IN  DESERT  PLANTS. 


somewhat  chang-ed,  since  it  has  been  extended  to  include  the  medullary  rays 
of  both  wood  and  cortex.  The  org-anization  of  the  phelloderm,  which  may 
be  observed  in  stems  4  mm.  in  diameter,  also  modifies  the  chlorophyll 
distribution.  The  phellogen  extends  from  the  outer  part  of  the  subepider- 
mal palisade  layer  to  about  the  layer  of  cells  which  is  next  to  the  inner 
chlorophyll-bearing-  cells.     In  the  outer  cells  the  outer  ends  are  converted 


Fig.  6. — Ephedra  antisyphilitica:  A.  cross-section  of  green  branch,  a  detail  of 
which  is  shown  in  B.  B.  portion  of  stem  to  show  structure  of  chlorophyll  band 
of  cortex.  Foiiquieria  spleiideiis:  C,  transverse  section  of  stem  5  mm.  in  diameter; 
bases  of  stout  spines  which  entirely  encircle  stem  are  not  shown.  D,  section  of 
older  stem  in  which  the  chlorophyll  band  has  become  discontinuous  as  a  result  of 
the  stem's  growth  (see  text).     ^7;.  (5.,  cortical  chlorophyll  band;  earn.,  cambium. 

by  transverse  walls  into  phellogen;  in  the  inner  cells,  however,  which  have 
the  long  axis  parallel  to  the  surface  in  stems  of  this  size,  the  division  walls 
forming  the  i)hellogfen  are  parallel  to  the  long  diameter  of  the  cells.  The 
bark  thus  orig-inating-  is  lens-shaped.  It  therefore  happens  that  a  cross- 
section  of  a  stem  4  mm.  in  diameter  shows  a  portion  of  the  primitive  cortex 
with  chlorophyll-bearing-  cells  and  a  portion  of  it  converted  into  cork  which 


EPHEDRA    ANTISYPHILITICA.  15 

is,  of  course,  without  chloroi)hyll.  However,  at  this  time,  in  addition  to 
segfments  of  the  orig-inal  chlorophyll  band,  there  extends  beneath  the  cork  at 
least  one  layer  of  cells  which  are  chlorophyllaceous.  It  does  not  appear 
that  the  phelloderm  contributes  to  the  chlorophyll  apparatus.  From  these 
circumstances  it  happens  that  stems  which  appear  brown  or  g'ray  in  color  and 
oivc  no  visible  indication  of  chlorophyll  are,  however,  chlorophyllaceous. 

With  the  further  development  of  the  bark  the  primary  cortex,  except  the 
sing-le  layer  of  cells  which  contain  chlorophyll  and  which  lie  immediately 
within  the  phellog-en,  is  entirely  cut  off,  and  with  this  process  the  most 
considerable  portion  of  the  chlorenchyma  of  the  stem  disappears.  When 
chlorophyll  quite  left  the  stem  was  not  learned.  In  a  stem  7.5  mm.  in 
diameter,  in  which  no  trace  of  the  primary  cortex  remained,  chlorophyll 
was  to  be  seen  in  the  outer  medullary  rays  of  the  woody  cylinder,  in  the 
rays  of  the  cortex,  and  sparingly  in  parenchyma  connecting  the  ends  of  the 
latter.  Stems  1.1  and  1.5  cm.  in  diameter  give  no  trace  of  chlorophyll  in 
either  wood  or  pith. 

FOUQUIERIA  SPLENDENS.      (Fig.  6.) 

Fouqiueria  occurs  on  dry,  well-drained  slopes.  The  plant  used  in  this 
study  is  growing-  on  Tumamoc  Hill  not  far  below  the  Laboratory. 

The  young-  stem,  5  mm.  in  diameter,  is  characterized  by  three  well- 
defined  areas,  namely,  (l)  an  external  shell  of  sclerenchyma,  within  which 
is  (2)  parenchyma  containing  chlorophyll,  and  within  this  is  (3)  the  inner 
cortex,  wood,  and  pith.  The  relative  extent  of  the  three  divisions  will  be 
apparent  from  the  sketches.  The  external  shell  is  part  of  the  primary 
cortex  and  is  morphologically  the  base  of  the  spines  of  the  stem,  which  in 
turn  are  morphologically  midribs  of  the  primary  leaves.  The  cells  of  the 
external  shell  early  take  on  the  characteristic  thickening  and  turn  brown, 
and  in  stems  5  mm.  in  diameter  the  shell  forms  a  continuous  covering. 
When  the  stem  increases  in  diameter,  however,  the  mass  of  sclerenchyma 
connected  with  each  spine  draws  away  from  the  mass  connected  with  every 
other  spine,  and  the  intervening-  space  is  occupied  by  a  waxy  tissue  which 
is  somewhat  greenish.  The  area  covered  by  these  two  classes  of  tissue 
is  more  and  more  disproportionate  in  amount  as  the  stem  grows  until  in 
the  oldest  parts  the  surface  is  practically  all  covered  by  the  newer  tissue. 

The  chlorophyll  is  confined  to  the  parenchyma,  which  lies  immediately 
within  the  shell  of  sclerenchyma  or  the  newer  tissue  that  succeeds  it.  It 
is  composed  wholly  of  cuboid,  thin-walled  cells  with  prominent  intercellular 
spaces. 

So  far  as  I  have  observed,  chlorophyll  is  always  present  in  the  stems  of 
Fouquieria,  of  whatever  size.  In  stems  5  mm.  in  diameter  the  chlorophyll 
band  forms  a  continuous  ring  in  the  outer  portion  of  the  cortex.  As  the 
shell  base  of  each  spine  becomes  separated  from  the  base  of  the  other  con- 
tiguous spines  in  the  manner  above  described,  breaks  occur  in  the  chloro- 


16 


TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IN   DESERT  PLANTS. 


phyll  band  opposite  the  center  of  each  sclerenchyma  mass,  due  perhaps  to 
the  fact  that  the  covering-  of  the  chlorophyll  band  at  that  point  is  heavy  and 
opaque,  so  that  the  chlorophyll  in  the  older  stems  occurs  opposite  the  newer 
external  tissue  only  (fig-.  6,  d).  This  circumstance,  together  with  the 
translucent  condition  of  the  newer  portion  of  the  external  covering,  is  largely 
responsible  for  the  green  coloring-  of  the  older  parts  of  the  plant. 
The  following  measurements  were  taken: 


Diameter 
of  stem. 

Width  of 
exterior 
covering. 

Depth  of 
chlorophyll 
in  the  stem. 

mm. 
5 
8 
30 

498 

500 

1162 

818 
894 

Franseria  dumosa.     (Plate  3,  b,  and  fig  7.) 

Franscria  is  a  globoid  shrub  about  50  cm.  high  which  is  growing  in  some 
abundance  on  the  north  slopes  of  Tumamoc  Hill  and  on  the  aerial  moun- 
tain-deltas in  the  western  portion  of  the  Laboratory  reservation.  It  is 
characterized  by  numerous  slender  branches  of  approximately  equal  length, 
which  spring  either  from  the  short  main  stem  or  from  the  bases  of  the 
older  branches .  It  thus  happens  that  new  branches  may  replace  dead  ones 
and  maintain  the  usual  form  of  the  plant  when  the  latter  fall  away.  The 
triangulate  leaves  are  sage-colored,  and  for  the  most  part  are  borne  near 
the  tips  of  the  branches,  although  there  is  great  variation  in  this  reg-ard, 
depending  apparently  on  the  adequacy  of  the  water-supply.  In  times  of 
extreme  drought  only  small  leaves  remain  on  the  very  tips  of  the  branches. 

The  external  tissues  of  the  branch  var.\-  with  its  age  and  presumably 
with  the  conditions  under  which  growth  took  place.  The  most  recent  por- 
tions are  green  and  dark  purple  in  color.  The  surface  has  a  shining  or  waxy 
appearance,  due  to  secretions  from  hairs,  certain  of  which  are  provided  with 
chlorophyll  (fig.  7,  c).  Below  the  younger  portions  the  branch  is  rough- 
ened by  narrow  longitudinal  furrows  and  ridges,  the  latter  of  which  are 
continuations  of  the  epidermis.  This  condition  marks  the  first  appearance 
of  bark.  Towards  the  base  of  the  stem  the  furrows  widen,  the  ridges 
disappear,  and  the  entire  surface  becomes  black  and  of  a  shaggy  character. 
As  will  be  shown  below,  chlorophyll  occurs  in  the  cortex  up  to  the  last  con- 
dition of  the  bark  given.  AVith  scarcely  an  exception  chlorophyll  is  found 
in  the  cortex  within  2  to  5  cm.  of  the  bases  of  the  secondary  branches,  from 
which  it  follows  that  a  very  large  percentage  of  the  entire  carbon  assimi- 
lative area  of  this  plant,  as  Foiiquieria  and  others,  must  be  in  its  branches. 

The  general  stnictural  characteristics  of  the  branches,  particularly  of  the 
cortex,  are  indicated  by  the  accompanying  sketches  and  may  be  outlined 


Cannon 


Plate     3 


A.—  KdBERLINIA   SPINOSA.     Branch  from  a  plant  which   is  situated  on  the  old    Ft. 
Yuma  Road  along  the  bottom  land  of  the  Santa  Cruz  River.      Nov.  8,   I  906. 

B. —  FRANSERIA   DUMOSA.     An  entire  plant  taken  from  the  northern   slope  of  the 
Tumamoc  Hill.      April  25,   1907.      Franseria  is  an  evergreen. 


FRANSERIA    DUMOSA. 


17 


as  follows:  The  epidermis  has  a  relatively  thin  cuticle.  At  a  distance  of 
1.5  cm.  from  the  tip  its  contents  are  colorless,  but  in  the  older  parts  a  dark 
purple  pigment  is  present.  As  previously  mentioned,  multicellular  hairs 
and  other  hairs  occur;  these  are  to  be  found  most  abundant,  perhaps,  where 
no  pigment  is  present  in  the  epidermis.  The  secretion  from  these  hairs, 
which  is  soluble  in  chloroform  and  ether,  is  so  copious  as  to  nearly  sub- 
merge them,  and  covers  the  stem  as  far  as  the  location  of  cork.     The  cortex 


Fig.  7. — Franseria  dumosa:  A, 
transverse  section  of  stem  1.23 
mm.  in  diameter,  showing 
general  distribution  of  chloro- 
phyll; 5,detail  of  A,  to  show 
character  of  cortical  chloren- 
chyma;  C,  secreting  hair  from 
young  part  of  stem,  to  show 
presence  of  chlorophyll,  which 
is  indicated  by  stippling,  on 
periphery  of  cells.  The  cells 
of  the  epidermis  do  not  con- 
tain chlorophyll. 


in  stems  1.23  mm.  in  diameter  and  5  cm.  from  the  tip  is  composed  of  four 
well-defined  tissues,  which,  enumerated  from  without,  are  collenchyma, 
parenchyma,  hard  bast,  and  soft  bast.  The  collenchymatous  and  the  par- 
enchymatous portions  are  chlorophyll-bearing;  some  chlorophyll  may  also 
be  found  in  the  ground-tissue  between  the  hard  bast  and  the  cambium. 
The  parenchyma  exterior  to  the  hard  bast  contains  chlorophyll  and  is  made 
up  of  cuboid  cells  with  large  intercellular  spaces. 


18 


TOPOGRAPHY  OF  CHLOROPHYLL  APPARATU.S  IN  DESERT  PLANTS. 


Except  in  the  very  yoiing-est  branches,  /.  i\,  those  less  than  1.13  mm.  in 
diameter,  no  chlorophyll  occurs  either  in  pith  or  wood,  but  in  a  section  of 
this  diameter  it  Avas  observed  in  both.  It  occurred  in  the  outer  cells  of  the 
pith  and  in  the  primary  medullary  rays  of  the  wood,  as  well  as  in  paren- 
chyma between  the  ducts. 

The  formation  of  cork  and  the  activit\-  of  the  cambium  make  imi^ortant 
modifications  in  the  chlorophyll  apparatus  as  above  described.  The  cork 
cuts  off  all  tissue  exterior  to  the  ring-  of  hard  bast.  There  does  not  api)ear 
to  be  a  definite  cork-cambium,  but  the  cortical  cells  are  directly  converted 
into  cork.  About  the  time  cork  is  formed  the  parench>-matous  cells  within 
the  hard-bast  ring-  become  much  enlarged,  the  chlorophyll  content  is 
g-reatly  increased,  and  these  cells  replace  in  function  the  primary  chloro- 
phyll band,  which  has  become  cork.  Through  the  activity  of  the  cambium 
more  deeply  placed  chlorenchyma  and  hard-bast  ring-s  are  formed,  which 
eventually  replace  the  secondary  chlorenchyma  much  as  the  latter  has 
replaced  the  primary  chlorenchyma.  The  exfoliating-  process  appears  to 
be  repeated  several  times,  until  in  the  oldest  portions  of  the  branch  the 
portions  cut  off  and  those  reformed  no  longer  contain  chlorophyll.  In  this 
repeated  formation,  destruction,  and  reformation  of  chlorench\-ma  Franscria 
is  peculiar  among  the  plants  observed. 

The  following-  measurements  were  made: 


Diameter 
of  branch. 

Distance 
of  section 
from  tip. 

Deptii  of 

outer  c 111 or- 

ophyll 

band. 

Width  of 
cortex. 

mm. 
'■13 
1.23 
1.67 
2.46 

cm. 
1-5 
5 
1 1 

15 

21 

126 
231 

294 
525 
588 

KcEHERLiNiA  SPiNOSA.     (Plate  3,  A,  and  fig.  8.) 

Kirlnr/liiia,  leafless  excei)t  in  seedling  stage,  occurs  as  isolated  plants 
mainly  in  the  bottom-lands  of  the  river.  It  avoids  for  the  most  jxirt  the 
dry  slopes  of  the  moimtains  and  the  mesa.  The  plant  studied  is  growing- 
near  the  southeast  comer  of  the  cemetery  at  Tucson.  It  is  about  1.5  m. 
high  and  extends  horizontally,  so  that  the  diameter  of  the  shrub  may  perha]xs 
be  3  m.     The  shrub  has  in  consequence  a  squat  appearance. 

In  structure  Kccberlinia  shows  several  striking-  characters.  A  cross- 
section  of  a  branch  3.5  mm.  in  diameter  and  5  cm.  from  the  tip  has  in  the 
cortex  four  well-marked  regions .  It  is  bounded  by  an  epidermis  with  a 
very  heavy  cuticle,  from  80  to  96  m  thick,  which  is  pierced  by  stomal  canals, 
immediately  beneath  the  epidermis  and  reaching  to  it  is  a  band  of  chlorophyll 
nearly  0.2  mm.  in  breadth.     This  band  is  btninded  on  its  inner  surface  by 


KCEBERLINIA    SPINOSA. 


19 


a  ring-  of  mechanical  tissue  composed  of  hard  bast  connected  by  grit-cells, 
and  within  this  ring-  is  the  thin- walled  parenchyma,  which  separates  the 
hard-bast  ring-  from  the  cambium.  Medullary  rays  reach  to  the  ring-  of 
mechanical  tissue.  The  wood  and  the  pith  exhibit  no  features  of  interest  in 
this  study. 


ch.h. 


Fig.  8. — Kivberlinia  spinosa:  Segment  from  cross-section 
of  stem  1.5  mm.  in  diameter,  to  show  distribution  of 
chlorophyll. 

The  chlorophyll  is  practically  wholly  limited  to  the  cortex.  If  it  is  found 
in  the  wood  at  all  it  is  in  the  outermost  medullary  rays.  The  most  impor- 
tant chlorophyll-bearing-  tissue  is  the  subepidermal  band  which  occupies 
the  area  between  the  epidermis  and  the  hard-bast  ring-.  The  outer  cells 
are  palisade  in  form;  the  inmost  three  layers  are  spong-y  chlorenchyma  or 
they  may  be  elongated  in  a  tang-ential  direction.  The  parenchyma,  which 
occurs  opposite  the  g-rit-cells,  and  therefore  between  the  hard-bast  groups, 
although  forming-  a  part  of  the  chlorophyll  band,  are  morphologfically  the 
outer  ends  of  the  cortical  mediillary  rays.  The  cells  referred  to  are  exterior 
to  the  grit-cells  and  have  become  detached  from  the  medullary  rays  by  the 
assumption  of  heavy  walls  by  that  part  of  them  which  lies  between  the 
hard-bast  groups. 

With  increased  diameter  certain  changes  in  the  relations  of  the  chloropyll- 
bearing  tissues  of  the  stem  take  place.  The  heavy  cuticle  becomes  ruptured 
at  frequent  intervals  and  the  spaces  thus  formed  are  covered  by  a  many- 
layered  periderm.      The  cork-cambium  arises  in  the  epidermis.     As  more 


22 


TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IN  DESERT  PLANTS. 


Olneya  TESOTA. 


OIncya  is  a  small  tree  of  whieh  but  a  sin.i;-le  specimen  is  gTowins"  near 
the  Laboratory  domain.  There  is  a  grove  of  this  speeies  at  Robles  Pass, 
Tucson  Mountains,  and  another  east  of  Pima  Canyon,  Santa  Catalina  Moun- 
tains. These  habitats  are  rocky  lower  mountain  slopes;  it  does  not  occur 
in  this  vicinity  on  the  bottom-lands  of  the  river  or  on  the  mesa. 

Branches  1.5  mm.,  4  mm.,  5.5  mm.,  9  mm.,  1.15  cm.,  1.35  cm.,  and 
2  cm.  in  diameter  were  studied;  the  sections  were  cut  the  following'  dis- 
tances from  the  tip:   1,  20,  35,  50,  65,  90,  and  120  cm. 

A  stem  1.5  mm.  in  diameter  is  characterized  by  an  epidermis  not  well 
defined,  by  a  chlorophyll  band  that  is  frequently  interrupted  by  masses  of 
collench^-ma,  and  by  a  relatively  narrow  inner  cortical  portion.  The  wood 
has  a  largfe  proportion  of  wood  parenchyma.  The  medullary  rays  extend  to 
the  chlorophyll  band  of  the  cortex  through  the  gaps  in  the  hard-bast  ring-. 

In  addition  to  there  being  chlorophyll  in  the  so-called  chlorophyll  band 
of  the  cortex,  it  is  to  be  found  in  branches  1.5  mm.  in  diameter  in  the 
medullary  rays  of  the  cortex,  but  not  in  the  wood  or  the  pith.  In  branches 
4  mm.  in  diameter  and  20  cm.  from  the  tip,  however,  chlorophyll  was  seen 
in  the  medullary  rays  of  the  wood  and  in  the  wood  parenchyma . 

A  characteristic  change  in  the  distribution  of  the  chlorophyll  in  the  stem 
and  in  its  relations  to  various  tissues  takes  place  with  increase  in  diameter. 
As  the  circumference  becomes  greater  the  groups  of  hard  bast  are  pulled 
farther  and  farther  apart,  the  spaces  between  are  filled  with  parench\'ma, 
and  as  this  tissue  is  really  the  distal  ends  of  the  medullary  rays,  the  latter 
in  older  stems  become  fan-shaped.  This  condition  recalls  that  observed  in 
Celtis  and  in  Prosopis.  The  chlorenchyma  is  increased  in  amount  by  the- 
activity  of  the  cork-cambium  also.  Periderm  is  to  be  seen  in  stems  9  mm. 
in  diameter.  It  is  formed  by  the  subepidermal  phellogen,  which  also  gives 
rise  to  phelloderm  that  contains  chlorophyll.  In  the  older  stems  the  chloro- 
phyll band  is  about  one-half  periderm  and  one-half  primary  cortex. 

The  chlorophyll  early  disappears  from  the  woody  cylinder.  In  a  branch 
9  mm.  in  diameter  it  could  be  found  in  neither  pith  nor  wood,  and  in 
branches  2  cm.  in  diameter  it  was  confined  to  the  outer  portion  of  the  cortex 
and  did  not  appear  to  be  functional. 

The  following  measurements  were  taken: 


Distance 
from  tip. 

Diameter 
of  branch. 

^%m. 

mm. 

-7^20 

'•5 

4 

-"  35 

5-5 

—   50 

9 
1. 15 

90 

'•35 

120 

20 

Width  of 
cortex. 


Width  of      Depth  of 

chlorophyll  i  chlorophyll 

band.  band. 


415 
498 
780 
1079 
1 162 
1660 


48 

So 

54-4 
118. 4 
160 
160 
160 


PARKINSONIA. 


23 


I   I  a  U 
^^M  I// 


^c    O 


A 


W 


'^^^. 


^^^^^ 


PARKINSONIA    ACULEATA,  P.  MICROPHYLLA,  AND    P.  TORREYANA. 

(Plate  4  and  figs.  lo  and  ii.) 

Parkinsonias  are  small  trees  which  occur  in  this  vicinity  in  habitats  that 
nsually  are  distinct.     P.  aculeata  is  found  native  on  the  lower  slopes  of  the 

Coyote  Mountains, about 
50  miles  west  of  Tucson, 
but  is  cultivated  in  the 
.gardens  of  the  city.  P. 
niicropJiylla  occurs  on 
Tu  manioc  Hill  and  on 
the  low,  dry  hills  in  the 
western  portion  of  the 
Laboratory  domain.  P. 
torreyana  is  growing-  in 
the  wash  at  the  western 
base  of  Tumamoc  Hill. 
The  three  species  are 
green  in  all  parts,  from 
which  the  common 
name,  pah  verde,  is  de- 
rived. P.  aadeata  and 
torreyana  carry  more 
leaf -surface,  or  at  least 
larger  leaves,  than  mi- 
crophylla,  in  which  they 
arc  extremely  small.  In 
each  species  portions  or 
all  of  the  leaves  fall  away 
during  unfavorable  sea- 
sons .  The  general  struc- 
tural relations  of  the 
stem  do  not  need  special 
notice;  they  will  be  ap- 
parent from  the  discus- 
FiG.  10— Parkhisoma  microphylla:  A,  segment  of  stem  sion  of  the  chlorophyll 
3  mm.  in  diameter;  ^,  transverse  section  of  woody  cylinder  apparatus, 
to  show   presence  of  chlorophyll  in  wood   parenchyma     ^^  ' 

adjoining  a  duct  and  in  the  medidlary  rays.  As  in  all  the  Young  branches,  i.e., 
other  sketches  the  stippling  indicates  the  presence  of  ^^ose  1  cm.  or  less 
^    ^^'^^  ^  '  in   diameter,  are  abun- 

dantly supplied  with  chlorophyll,  which  is  distributed  in  characteristic  fash- 
ion from  epidermis  to  pith.  In  general  terms  this  distribution  may  be 
defined  as  follows:  It  occurs  in  the  cortex  as  three  separate  bands  concen- 
trically placed  in  the  medullary  rays  of  cortex  and  of  wood,  in  certain  of 
the  wood  parenchyma,  and  in  the  pith.     This  is  the  maximum  chlorophyll 


o 


M  111     i^o-o 


0(DOobcpo 


o 


24         TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IN  DESERT  PLANTS. 


distribution,  but  in  older  stems,  owin.q:  to  chang-es  in  structure  incident  to 
growth  and  development  by  which  the  various  chlorophyll-bearing-  tissues 
are  ehminated  or  lose  their  chlorophyll  contents,  this  distribution  is  greatly 
modified. 

The  epidermis  is  usually  or  at  least  frequently  well  supplied  with  chloro- 
phyll. This  applies  to  stems  1  cm.  or  less  in  diameter,  although  a  branch 
of  P.  torreyana  was  examined  which  was  2.25  cm.  in  diameter  and  which, 
nevertheless,  still  had  chlorophyll  in  the  epidermis.  It  may  be  remarked  in 
passing  that  this  branch  showed  another  characteristic  which  is  unusual  in 
Parki7isonia—t'he  woody  cylinder  did  not  contain  chlorophyll.  As  will 
appear   later,  in   the  ordinary  se- 


quence of  the  disappearance  of 
chlorophyll  from  the  stem,  the  epi- 
dermis leads,  followed  by  the  pith 
and  the  wood. 

The  most  prominent  mass  of 
chlorophyll-bearing  tissue  in  the 
stem,  and  the  one  that  gives  the 
color  characteristic  of  the  tree,  is 
the  outer  cortical  chlorophyll  band. 
Also,  this  chlorophyll  tissue  is  the 
most  enduring.  It  has  been  iden- 
tified in  stems  8  cm.  in  diameter, 
and  is  present  in  the  oldest  parts, 
even  in  some  or  perhaps  most  instances  within  a  few  centimeters  of 
the  very  base  of  the  tree.  It  varies  in  width  from  83  /^  to  246  /*  and  its  outer 
surface  lies  from  83  /^  to  500  ^  beneath  the  surface  of  the  stem.  In  stnicture 
the  chlorophyll  band  is  wholly  of  spongy  tissue.  The  cells  are  cuboid  and 
thin- walled. 

Within  the  outermost  band  of  chlorenchyma  is  a  ring  of  mechanical  tissue 
composed  of  alternating  groups  of  hard  bast  and  of  heavy-walled  paren- 
chyma (which  later  become  grit-cells?).  A  second  band  of  chlorenchyma 
lies  immediately  within  this  mechanical  stratum,  which  for  convenience 
will  be  termed  the  median  band  of  chlorenchyma.  In  the  younger  stems  the 
median  band  is  practically  continuous,  but  in  the  older  ones  it  becomes 
broken  up  into  distinct  masses.  From  the  median  band  there  passes  inward, 
like  the  spokes  of  a  wheel,  the  medullary  rays  of  the  inner  part  of  the  cortex. 
These  rays  in  the  younger  branches  are  well  supplied  with  chlorophyll. 

Turning  now  to  the  woody  cyHnder,  we  find  that  the  medullary  rays,  a 
portion  of  the  wood  parenchyma,  and  the  pith  are  chlorophyll-bearing.  In 
branches  1  cm;  in  diameter  the  entire  medullary  ray  from  cortex  to  the  pith 
is  so  well  provided  with  chlorophyll  that  the  cut  end  of  the  branch  under 
a  hand-lens  appears  grass  green.  In  much  larger  stems,  however,  and  in 
smaller  ones  from  a  less  healthy  plant  no  chlorophyll,  or  scarcely  any,  is  to 


Fig.  II. — Parkitisonia  torreyana:  Segment 
of  stem  7  mm.  in  diameter,  to  show  the 
distribution  of  chlorophyll.  Lettered  as  in 
preceding  figures. 


Cannon 


Plate    4 


PARKINSONIA   MICROPHYLLA.      The  species  from  which  this  branch  was  taken 
deciduous  ;   the  branches  are  green  and  function  as  leaves.     April  25,  I  907. 


PARKINSONIA. 


25 


be  found  in  the  wood.  The  wood  parenchyma  in  the  immediate  vicinity 
of  the  ducts  may  contain  chlorophyll  (fig-.  10). 

As  to  chlorophyll  in  the  pith,  it  need  only  be  said  that  it  occurs  sparingly 
in  stems  1  cm.  in  diameter  and  is  not  present  in  the  older  and  larger  branches. 

The  chlorophyll  disappears  from  the  stem  in  a  very  regular  seciuence. 
It  leaves  the  epidermis  first,  then  the  pith,  then  the  inner  medullary  rays; 
after  this  the  wood  parenchyma,  then  the  medullary  rays  of  the  cortex  and 
the  median  band,  and  finally,  when  cork  is  formed,  the  outer  band.  That 
is,  with  two  exceptions,  the  chlorophyll  disappears  from  the  stem  in  a  cen- 
trifugal direction.  The  exceptions  were  most  marked  in  stem  of  P.  torreyana 
8  mm,  in  diameter,  in  which  practically  all  of  the  chlorophyll  of  the  pith, 
as  well  as  of  the  medullary  rays  of  the  wood,  had  been  removed,  but  the 
deeply-placed  wood  parenchyma  near  the  ducts  still  contained  chlorophyll 
in  considerable  quantity. 

The  leading-  departures  from  the  chlorophyll  conditions  shared  in  common 
by  the  three  species  of  Parkinsonia  are  as  follows:  P.  aaileata:  Branches 
7  and  12  mm.  in  diameter  had  no  chlorophyll  in  pith  or  in  the  inner  part 
of  the  wood.  P.  microphylla:  A  variation  due  possibly  to  differences  in 
water  relations  was  observed  in  branches  1  cm.  in  diameter.  One  branch, 
taken  from  a  tree  which  was  apparently  poorly  supplied  with  water,  had 
very  little  chlorophyll  in  the  wood  and  none  in  the  pith,  while  another 
branch  of  the  same  diameter,  taken  from  a  tree  that  had  been  irrigated  at 
frequent  intervals,  had  the  maximum  distribution  of  chlorophyll.  P.  tor- 
reyana: As  may  be  implied  from  a  previous  statement,  this  species  appears 
not  usually  to  have  so  much  chlorophyll  in  its  branches  as  the  other  ones, 
but  an  exception  was  noted  in  a  stem  2.25  cm.  in  diameter,  in  which  the 
chlorophyll  was  in  the  epidermis  and  extended  into  the  stem  for  a  distance 
of  6  mm.  This  tree  was  growing  in  a  particularly  favorable  location  in 
the  wash  at  the  west  base  of  Tumamoc  Hill. 

The  following  measurements  were  made: 


Species. 

Diameter 
of  branch. 

Outer  cortical  band. 

Penetration 
of  chloro- 
phyll. 

Depth. 

Width. 

P.  aculeata 

mm. 

7 

M 

•"s; 

M 

960 
83 

130 
144 

^^^ 

160 
144 
176 
160 
196 
224 

mm. 
0.6 

1-5 
0.5 
1.8 

'■) 
1.6 

2 

5 

6 
0.4 

Do 

,o 

Do 

II-5 
15 

32-5 
49 
8o 
8 

lO 
12-5 

22.5 
30 

144 
1 12 
160 
130 
160 
64 
96 
96 
96 
128 

Do 

Do    

Do 

Do 

P.  torreyana 

Do. 

Do 

Do 

Do. 

26         TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IN  DESERT  PLANTS. 
Prosopis  VELUTINA.     (Figs.  12,  13,  and  14.) 

Prosopis  vehdina  is  the  most  characteristic  tree  of  the  river-bottoms,  where 
in  places  it  forms  extensive  forests.  It  varies  in  size  from  a  small  shrub 
to  a  well-formed  and  shapely  tree  15  m.  or  more  higfh.  The  difference  in 
size  depends  mainly  on  the  lack  or  the  abimdance  of  the  water-supply. 
Leaves  are  fomied  in  the  sprint-  and  arc  shed  in  the  autumn  witli  a  rc.i^u- 
larity  characteristic  of  deciduous  trees  of  more  humid  regions. 


CD- 


•".<■•■ 


Fig.  12. — Prosopis  veliitina:  A,  transverse  section  of  stem  4  mm.  in  diameter, 
to  show  distribution  of  chlorophyll;  5,  segment  from  cortex  of  stem  7  mm. 
in  diameter,  to  show  relation  of  hard  bast  (h.  b.)  to  chlorophyll. 

The  sections  of  branches  studied  were  cut  at  nine  separate  intervals 
from  3  cm.  to  1.23  m.  from  the  tips,  and  were  from  1.3  mm.  to  1.5  cm.  in 
diameter. 

In  several  particulars  the  distribution  of  chlorophyll  in  Prosopis  recalls 
that  in  Parkinsonia.  In  the  young  stem  chlorophyll  maybe  found  in  prac- 
tically all  of  the  g-round-tissue  both  of  cortex  and  of  wood.  With  increase 
in  size  the  chlorophyll  distribution  of  the  stem  becomes  greatly  restricted 
and  the  topography  of  the  chlorophyll  apparatus  becomes  much  changed. 
The  general  structural  relations  of  the  stem  will  be  apparent  from  the  suc- 
ceeding accoimt  of  the  distribution  of  the  chlorophyll  and  will  not  require 
especial  discussion. 

The  epidermal  cells  of  Prosopis  do  not  contain  chlorophyll  — in  this  as 
well  as  certain  other  i^articulars  Prosopis  is  imlike  Parkinsonia.      Prosopis 


PROSOPIS   VELUTINA. 


27 


stems  older  than  one  year  have  in  the  cortex  a  varying-  number  of  concen- 
trically placed  hard-bast  rings  which  are  broken  at  intervals  where  the 
medullary  rays  penetrate  the  cortex.  Between  the  rings  of  hard  bast  is  to 
be  found  a  thin-walled  parenchyma.  It  is  the  disposal  of  the  hard  bast, 
tog-ether  with  the  disposal  of  this  parenchyma,  that  in  stems  4  cm.  in 
diameter  and  less  determines  the  character  of  the  distribution  of  chlorophyll 
in  the  inner  portion  of  the  cortex.  A  cross-section  of  a  stem  4  mm.  in 
diameter  shows  the  chlorophyll -bearing-  cells  of  the  cortex  arranged  in  the 
gfeneral  form  of  a  net,  in  which  what 
may  be  called  the  warp  is  the  med-  cTub. 

iillary  rays  and  the  woof  the  par- 
enchyma, or  that  portion  of  the 
parenchyma  that  separates  the 
rings  of  hard  bast.  The  woof  of 
the  texture  in  young  stems  occurs 
along  the  inner  side  of  the  second- 
ary hard-bast  rings,  but  in  older 
stems,  for  reasons  g-iven  below,  it 
occupies  practically  the  entire  space 
between  the  bast  grroups. 

With  increase  in  size  of  the  stem 
certain  changes  occur  in  the  chlor- 
ophyll apparatus  which  are  depend- 
ent on  the  dispositon  of  the  other 
cortical  tissues.  As  the  circum- 
ference of  the  stem  becomes  greater 
the  g-roups  of  bast  become  farther 
apart,  while  at  the  same  time,  as 
a  result  of  the  radial  pressures  set 
up,  the  rings  are  approximated 
nearer  and  nearer  to  each  other. 
The  most  notice  able  effects  of  these 
changes  occur  naturally  in  the  more 
peripheral  portions  of  the  cortex. 
The  primary  medullary  rays  in 
young  stems  extend  to  the  hard-bast  ring,  and  when  by  the'growth  of  the 
stem  this  is  broken  up  and  its  members  are  connected  by  stony  tissue  the 
rays  extend  to  the  stoity  tissue  of  this  ring-.  Secondary  hard-bast  ring-s  are 
formed  within  the  primary  one,  between  the  segments  of  which  pass  the 
medullary  rays.  With  the  growth  of  the  stem  the  outer  g-roups  of  sec- 
ondary bast  separate  from  one  another,  just  as  happened  with  the  primary 
bast  groups,  and  the  more  peripheral  rings  become  closely  pressed  together. 
These  general  relations  not  easily  described  will  be  apparent  from  the 
sketches. 


Fig.  \2.—Prosopis  velutina:  Detail  from  in- 
ner portion  of  cortex  of  stem,  to  show 
structure  of  distal  ends  of  medullary  rays 
and  connection  between  outer  mass  of  chlo- 
rophyll {ch.  b.)  and  the  more  deeply  lying 
chlorenchyma.  h.b.,  hard  bast;  ch.  b.,  cor- 
tical chlorophyll  band. 


28         TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IN  DESERT  PLANTS. 


In  the  young-  stem  the  medullarj'  rays  of  the  cortex  are  about  one  cell 
wide,  but  as  the  hard-bast  groups  separate  from  each  other  with  the  gfrowth 
of  the  stem  the  rays  broaden  to  fill  out  the  resulting-  gaps  until  the  ends 
are  many  cells  wide.  The  most  striking  effect  is  associated  with  the  pri- 
mary rays.  They  feel  the  effects  of  the  growth  sooner  than  the  other  rays 
and  of  a  consequence  the  ends  of  the  primary  medullary  rays  are  fan- 
shaped  and  present  in  cross-section  a  very  striking-  appearance.  From  this 
manner  of  differentiation  and  development  of  tissues  the  amount  of  chloren- 
chyma  in  the  young  cortex  is  much  increased. 

Growth  of  the  stem  works  also 
to  modif}'  the  relations  of  the 
outer  chlorophyll  band  in  a 
way  that  may  be  noted.  In  a 
branch  1.3  mm.  in  diameter  an 
unbroken  ring  of  hard  bast 
sejxiratcs  the  chlorophyll  band 
from  the  inner  cortical  tissues. 
In  a  branch  4.5  mm.  in  diameter 
the  hard-bast  ring  becomes  bro- 
ken up  into  g-roups,  as  was  de- 
scribed above.  The  connecting- 
cells  at  first  with  thin  walls  be- 
come, finally,  stony  tissue  and 
contain  chlorophyll.  As  a  result 
the  outer  band  is  joined  to  the 
medullary  rays  and  practically 
the  entire  chlorophyll  apparatus 
is  welded  into  a  sing-le  tissue. 
Later,  however,  the  outer  band 
of  chlorophyll  becomes  ag-ain 
separated  from  the  inner  chlor- 
enchyma  by  the  further  devel- 
opment of  the  same  stony  tissue. 
As  in  Parkinsonian  chlorophj'll  occurs  in  the  medullary  rays  of  the  wood, 
in  the  parenchyma  of  the  wood,  and  in  the  pith.  In  order  of  disappearance 
it  leaves  the  pith  and  the  inner  medullary  rays  first;  it  ling-ers  behind  in 
the  parenchyma  surrounding  the  ducts.  The  exact  time,  however,  that 
the  chlorophyll  leaves  the  woody  cylinder  was  not  learned.  In  a  branch 
4  cm.  in  diameter  no  chlorophjdl  was  to  be  seen  in  the  wood,  and  it  did  not 
extend  deeper  than  0.5  mm.  beneath  the  surface  of  the  stem. 

The  later  history  of  the  chloro]:)hyll  apparatus  is  connected  with  the  for- 
mation of  bark.  This  is  one  of  the  factors  which  brings  about  the  changes 
in  appearance  of  the  stem  which  are  characteristic  of  it  at  different  times 
during-  development. 


i  c>  .Boo  a^ 

cam  .    ^^      _      ^ 

Fig.  14. — Prosopis  velutina:  Segment  of  stem 
1.5  cm.  in  diameter,  in  which  is  shown  ar- 
rangement of  rings  of  hard  bast  and  their 
relation  in  the  chlorophyll  apparatus. 


PROSOPIS   VELUTINA. 


29 


In  the  early  part  of  the  first  year  of  growth  the  branch  is  smooth  and  of 
a  dark  purple  color;  later  in  the  season  it  becomes  g^reen  and  is  flecked  with 
minute  purple  or  red  dots  and  is  somewhat  rough  to  the  touch.  During- 
the  following-  season  and  for  an  undetermined  period  afterwards  it  remains 
gfreen.  Finally  this  is  replaced  by  a  gray  surface  which  also  is  slightly 
rough  and  which  persists  for  several  years.  Branches  8  cm.  in  diameter 
may  have  this  appearance.  The  gray  exterior  is  in  turn  replaced  in  old 
stems  by  a  rough  bark  black  in  color. 

The  color  of  the  youngest  stem  is  due  to  red  and  blue  pigment  in  the 
epidermis,  and  the  texture  of  the  surface  to  the  unbroken  cuticle.  As  the 
stem  becomes  older,  phellogen  arises  in  the  epidermis,  which  forms  primary 
periderm  and  primary  phelloderm.  Ruptures  appear  in  the  cuticle,  which 
become  pronounced  and  allow  the  chlorophyll  to  be  seen  through  the  corky 
tissue.  As  the  stem  becomes  larger  the  amount  of  cork  increases,  the 
amoimt  of  phelloderm  especially  becomes  greater,  and  at  length  entirely 
conceals  the  underlying  chlorophyll.  This  condition  lasts  a  long  time  and 
constitutes  the  third  stage,  as  presented  above.  Finally,  in  still  older  stems 
a  secondary  phellogen  is  organized  deeper  in  the  cortex  than  the  chlorophyll 
band  and  separates  this  tissue  to  its  ruin  from  the  remainder  of  the  stem. 
After  the  formation  of  the  secondary  phellogen  the  stem  does  not  as  a  con- 
sequence contain  more  chlorophyll. 

The  following  measurements  were  taken: 


Diameter 
of  branch. 

Distance 
from  tip. 

Depth  of 
chlorophyll 

Width  of  '    Depth  of 

chlorophyll  chlorophyll 

band.       ;       band. 

mm. 

cm. 

mm. 

M 

M 

1-3 

A 

0.65 

32 

32 

1.6 

0.80 

32 

48 

2.25 

33 

125 

64 

64 

3-3 

48 

1.65 

64 

48 

4-5 

63 

2.25 

64 

48 

5 

7« 

2.32 

^ 

48 

7 

93 

3-30 

64 

48 

9 

108 

3-3° 

106 

32 

15 

123 

100 

48 

Salix  nigra. 


Salix  occurs  in  some  abundance  along  the  banks  of  the  bed  of  the  Santa 
Cruz  River.     Some  of  the  trees  may  attain  a  height  of  15  m.  or  more. 

A  section  of  a  branch  3.5  mm.  in  diameter  30  cm.  from  the  tip  shows  the 
following  general  relations  of  the  tissues:  Beginning  with  the  periphery 
there  is  (l)  a  protective  portion  about  four  cells  deep,  which  does  not 
contain  coloring  matter,  and  a  protective  portion  beneath  this  about  two 
cells  in  thickness  that  is  pigmented;  (2)  a  parenchymatous  tissue  which  is 
chlorophyllaceous;  (3)  groups  of  hard  bast  and  inner  ground-tissue  and 
cambium;  and  (4)  finally,  the  woody  cylinder. 


30  TQPOGRAPHV  OF  CHLOROPHYLL  APPARATUS  IX  DESERT  PLANTS. 

The  chlorophyll  occurs  in  the  parenchyma,  which  is  immediately  within 
the  many-celled  protective  layer  but  not  in  a  well-defined  band,  in  the 
medullary  rays  of  cortex  and  of  wood,  and  in  the  pith.  As  is  usually  the 
case  with  g-rowth  of  the  stem,  the  distribution  of  the  chlorophyll  is  chang-ed 
and  it  becomes  much  reduced  in  amount.  In  a  branch  8.5  mm.  in  diameter 
and  90  cm.  from  the  ti])  the  chlorophyll  was  confined  to  the  outer  portions 
of  the  medullary  rays  and  to  the  cortex;  and  in  a  branch  1.3  cm.  in  diameter 
and  150  cm.  from  the  tip  it  had  left  the  woody  cylinder  entirely  and  was  to 
be  foimd  onh-  in  the  subepidermal  chlorophyll  band.  The  fate  of  the 
chlorophyll  band  was  not  learned. 

SAMP.UCUS  MEXICANA.  .. 

Samd7(n/s occurs  as  scattered  individuals  by  roadsides  on  the  river-bottoms. 
It  forms  a  small  tree  from  5  to  8  m.  high,  with  a  main  stem  15  to  20  cm. 
in  diameter.  The  tree  which  was  selected  for  study  is  growing-  by  the 
Hospital  Road  east  of  the  Laboratory  domain.  It  is  about  6  m.  high 
and  has  a  polled  appearance,  as  if  most  of  the  shoots  were  second  growth. 

The  topogfraphy  of  the  chlorophyll  apparatus  presents  no  uniisual  char- 
acters. In  the  young-est  portions  of  the  branch,  2.5  mm.  in  diameter  and 
0.5  cm.  from  the  tip,  all  of  the  g-round-tissue  is  chlorophyll-bearing.  That 
is  to  say,  chlorophyll  is  to  be  found  from  the  epidermis  to  the  center  of  the 
extensive  pith  and  in  all  tissues  except  those  already  differentiated.  There 
appears  to  be  no  distinct  cortical  band.  The  chlorenchyma  is  made  up  of 
spongry  tissue,  which  for  the  most  part  has  very  thin  walls  and  prominent 
intercellular  spaces.  No  change  in  the  distribution  of  the  chlorophyll  is 
to  be  noted  until  the  stem  is  about  4.5  mm.  in  diameter,  when  none  may 
be  found  in  the  pith  and  but  little  in  the  inner  portion  of  the  cortex  outside 
of  the  medullary  rays.     It  occurs  in  the  medullary  rays  of  the  wood. 

When  chlorophyll  wholly  left  the  stem  was  not  determined.  In  a  branch 
8  mm.  in  diameter  and  25  cm.  from  the  tip,  chlorophyll  was  found  in  the 
parenchyma  of  the  primary  cortex  immediately  within  the  mechanical 
tissue  and  nowhere  else.  In  another  branch  1.6  cm.  in  diameter  and 
at  a  point  1.23  m.  from  the  tip  the  distribution  was  found  to  be  quite  the 
same. 

The  youngrest  portions  of  the  stem  are  frequently  green,  /.  e.,  there  is 
no  protective  covering  for  the  chlorophyll.  The  second  node  is  often  piirple 
from  a  red-blue  pigment  in  the  subepidermal  cells.  In  the  next  older  node 
there  may  in  addition  be  a  heavy  covering  of  trichomes.  Also,  the  cork- 
cambium  is  laid  down  early  in  the  development  of  the  branch  and  takes  its 
origin  in  the  subepidermal  cells,  so  that  it  happens  that  some  sort  of  pro- 
tection against  excessive  illumination  or  excessive  transjiiration,  either  the 
leafy  covering  of  the  stem,  pigmented  cells,  a  hairy  coating  of  the  epidermis, 
or  cork  is  q:iven  the  chlorcnchvma  during  its  entire  existence. 


ZIZYPHUS    PARRYI. 


31 


ZizYPHUS  PARRYI.     (Plate  5  and  fig.  15.) 

Zizyphus  occurs  sparingly  on  the  river-bottoms  or  elsewhere  where  the 
water  conditions  are  fairly  good.  It  is  a  grayish-colored  (due  to  hairy 
covering)  spiny  shrub  from  1.5  to  3  m.  high  and  bears  during  favorable 
seasons  a  considerable  leaf-surface.  As  is  the  case  with  the  most  of  the 
desert  perennials,  the  leaves  fall  away  with  the  advent  of  dry  conditions  and 
leave  the  shrub  bristling  with  spines  in  a  condition  very  much  like  the 
ordinary  condition  of  Koeberlinia  emoryi. 


Fig.  15. — Zizyphus  parryi:  Section  of  stem  3  mm.  in  diameter, 
to  show  distribution  of  chlorophyll,  ch.  (J., cortical  chlorophyll 
band;  h.  b.,  hard  bast;  ca/n.,  cambium. 

The  young-  stem  of  Zizyphus  shows  the  customary  divisions  into  cortex, 
wood,  and  pith,  of  which  the  latter  is  especially  abundant.  The  main 
divisions  of  the  cortex  are  the  epidermis  with  its  rather  heavy  cuticle,  a 
chlorophyll  band  beneath  the  epidermis,  a  hard-bast  ring-  which  is  discon- 
tinuous, and  the  g-roimd  tissue  between  it  and  the  cambium. 

The  distribution  of  the  chlorophyll  is  very  much  as  in  other  plants.  The 
outer  cortical  parenchyma,  most  of  the  inner  cortical  parenchyma,  the 
medullary  rays,  and  the  outer  pith-cells  contain  chlorophyll.  The  outer 
chlorophyll  band,  which  is  interrupted  at  frequent  and  fairly  reg-ular  inter- 
vals by  masses  of  collenchyma,  has  a  palisade  structure,  at  least  in  the 
outer  part,  of  short  cells  very  like  the  cells  in  the  leaf.  The  inner  chloren- 
chyma  cells  are  cuboid.  The  parenchyma  and  the  collenchyma  between 
the  chlorophyll  band  and  the  groups  of  hard  bast  deeper  in  the  cortex  con- 
tain chlorophyll.  The  medullary  rays  of  the  cortex  are  also  chlorophyll- 
bearing-.     The  rays  either  end  in  the  groups  of  hard  bast  or  pass  outward 


Z2 


TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IN  DESERT  PLANTS. 


between  them  and  join  the  broad  band  of  chlorophyll.  Chlorophyll-bearing: 
tissue  on  the  inner  face  of  the  ring  of  hard  bast  connects  the  medullary 
rays.  So  that  there  are  three  rings  of  chlorenchyma  in  the  cortex,  namely, 
the  chlorophyll  band  and  two  inner  rings  separated  by  hard  bast.  The 
medullary  rays  of  the  wood  and  of  the  pith  in  a  stem  3  mm.  in  diameter 
contain  small  amounts  of  chlorophyll. 

With  increased  diameter  certain  changes  in  the  distribution  of  the  chlor- 
ophyll occur  which  should  be  noted.  As  usual,  these  modifications  are 
most  marked  in  the  cortex.  With  lateral  stretching,  which  accompanies 
the  growth  of  the  stem,  the  groups  of  hard  bast  become  farther  and  farther 
apart  and  the  intervening  spaces  become  filled  with  a  chlorophyll-bearing 
tissue,  so  that  the  relative  and  actual  amount  of  chlorenchyma  is  much 
increased. 

In  stems  1.4  cm.  in  diameter  the  formation  of  cork  has  begun.  The 
phellogen  appears  to  take  its  origin  in  the  epidermis  and  shows  little  indi- 
cation of  activity.  Only  a  small  amount  of  periderm  was  observed  and 
almost  no  phelloderm.  The  periderm  in  the  larger  branches  is  colored  a 
deep  red  and  is  broken  through  at  intervals  by  lenticels.  No  chlorophyll 
is  to  be  found  in  wood  or  pith,  although  in  a  stem  1.55  cm.  in  diameter  and 
1.6  m.  from  the  tip  the  cortical  chlorophyll  band  was  still  to  be  seen. 
When  it  disappeared  from  the  stem,  if  ever,  was  not  learned. 

The  following  measurements  were  made: 


Diameter 
of  branch. 

Distance 
from  tip. 

width  of 
cortex. 

Width  of 

chlorophyll 

band. 

Depth  of 

chlorophyll 

band. 

7nm. 

cm. 

M 

M 

M 

3 

5 

192 

57.6 

19.2 

3-5 

20 

256 

76.8 

19.2 

4-5 

35 

262.4 

89.6 

19.2 

6 

SO 

381.8 

80 

22.4 

8 

80 

398.4 

73-6 

22.4 

14 

no 

664 

64 

41.6 

14-5 

140 

664 

64 

32 

15-5 

160 

747 

41.6 

35-2 

Can  I 


Plate  5 


'.m 


g^^ 


>^%i*. 


ZIZYPHUS  PARRYI.  Branch  from  a  plant  which  is  situated  by  the  St.  Mary's  Road 
near  the  laboratory  domain.  Zizyphus  is  a  plant  with  the  deciduous  habit. 
April  25,  1907. 


GENERAL   DISCUSSION.  33 

GENERAL  DISCUSSION  AND  RESULTS. 
MORPHOLOGY  OF  THE  CHLOROPHYLL-BEARING  TISSUES. 

Although  different  in  details,  the  g-^neral  arrangement  of  the  chlorophyll 
apparatus  in  the  stems  of  desert  perennials  has  in  many  respects  a  close 
similarity,  for  which  reason  the  type  aiTangement  can  be  presented  by 
describing  an  ideal  stem. 

The  ideal  branch  will  have  a  diameter  of  5  mm.,  with  the  following 
structural  divisions:  (l)  an  epidermis  with  a  relatively  heavy  cuticle; 
(2)  a  hypodermal  tissue  about  three  cells  in  thickness;  (3)  an  outer  cortical 
chlorophyll  band,  which  is  somewhat  wider  than  the  hypoderm  and  which 
lies  immediately  beneath  it;  (4)  a  hard-bast  ring;  (5)  the  inner  portion  of 
the  cortex,  in  which  are  the  distal  ends  of  the  medullary  rays,  perhaps 
secondary  hard  bast  and  undifferentiated  ground-tissue;  (6)  the  woody 
cylinder  and  the  pith.  Medullary  rays  are  prominent  and  wood  parenchyma 
is  present  in  considerable  amount. 

Such  being-  the  general  structural  relations  of  the  stem,  the  chlorophyll 
is  distributed  as  follows:  The  leading  chlorophyll-bearing  tissue  is  the 
subepidermal  band,  and  this  is  true  not  only  because  it  is  the  most  exten- 
sive of  the  stem,  but  also,  as  will  be  shown  below,  because  it  retains  chloro- 
phyll the  longest  of  any  of  the  tissues.  Moreover,  it  is  rarely  changed  into 
any  other  kind  of  tissue,  but  persists  as  chlorenchyma  until,  as  a  general 
thing,  it  is  cut  off  by  the  formation  of  cork. 

The  medullary  rays,  both  of  the  wood  and  of  the  cortex,  contain  chloro- 
phyll. The  distal  ends  of  the  medullary  rays  extend  into  the  cortex  and 
between  the  groups  of  hard  bast  and  abut  on  the  inner  face  of  the  chloro- 
phyll band,  by  which  circumstance  the  chlorenchyma  of  the  stem  is  for  the 
most  part  bound  into  one  continuous  system.  In  addition  to  the  chlorophyll 
band  and  the  distal  ends  of  the  medullary  rays,  there  is  in  the  cortex  another 
kind  of  chlorenchyma,  namely,  the  ground-tissue,  that  lies  immediately 
within  the  hard-bast  groups.  In  the  woody  cylinder,  in  addition  to  the 
medullary  rays,  the  wood  parenchyma  also  may  contain  chlorophyll.  This 
is  true  especially  of  those  cells  that  are  placed  near  the  ducts.  Lastly,  the 
pith  may  be  chlorophyllaceous.  Generally  speaking,  therefore,  with  the 
exception  of  certain  embryonic  tissues  in  the  cortex,  all  of  the  parenchyma 
of  the  stem  may  contain  chlorophyll. 

As  the  stem  increases  in  diameter,  certain  changes  in  these  tissues,  as  a 
whole,  and  in  those  which  are  chlorophyll-bearing,  are  seen  to  take  place, 
some  of  which  should  be  noted.  These  may  be  outlined  as  (l)  the  gradual 
disappearance  of  the  chlorophyll  and  (2)  as  modifications  in  the  topography 
of  the  chlorophyll  apparatus,  as  above  sketched. 

In  the  usual  condition  there  is  a  certain  order  in  the  recession  of  chloro- 
phyll in  the  stem.     This  is  as  follows:   It  disappears  first  from  the  pith; 


34         TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IN  DESERT  PLANTS. 

then  from  the  medullar}-  rays  of  the  wood,  beg"inning-  in  the  inmost  portions; 
then  from  the  wood  parenchyma;  after  this,  from  the  medullary  rays  of  the 
cortex;  and,  lastly,  from  the  chlorophyll  band,  or,  more  usually,  the  band 
itself  is  obliterated.  In  the  exceptional  event  of  chlorophyll  in  the  epidermis 
of  the  young-er  stem,  as  in  Parkinsonia,  this  may  leave  the  stem  before  any 
other  tissue  is  deprived  of  its  chlorophyll.  Generally  speaking-,  however, 
with  the  exception  of  the  wood  ])arenchyma,  the  chlorophyll  of  the  stem 
disappears  in  a  centrifugfal  fashion.  Possibly  the  exception  is  due  to  some 
favoring-  condition,  as  the  proximity  of  better  air-supply,  or  more  water, 
or  the  light  may  be  condensed  by  the  water-content,  so  that  a  portion  of  the 
contiguous  parenchyma  may  have  better  light  relations  than  that  in  the 
medullary  rays. 

The  chlorophyll  band  remains  active  until  its  organic  connection  with 
the  inner  living-  portions  of  the  cortex  is  severed  by  the  formation  of  cork, 
or  until  destroyed  by  pressure  occasioned  by  growth  of  the  stem.  In 
some  forms,  as  Ceretis  and  Parkinsonia,  as  a  rule,  it  is  never  destroyed  during 
the  life  of  the  plant,  but  persists  and  gives  the  color  characteristic  of  each. 

SPECIAL  STRUCTURAL  FEATURES. 

We  may  turn  now  from  a  review  of  what  may  be  called  the  general  con- 
dition of  the  stem  as  regards  the  distribution  of  chlorophyll  and  take  note 
of  phases  of  the  distribution  and  other  characters  of  the  chlorophyll-bearing 
tissues  not  shared  by  all  of  the  plants  examined. 

Attention  may  first  be  called  to  a  curious  modification  of  the  chlorophyll 
band  which  frequently  accompanies  increase  in  diameter  of  the  stem.  This 
is  associated  with  the  formation  of  cork.  The  chlorophyll  band,  properly 
so-called,  is  an  integral  portion  of  the  primary  cortex;  in  old  stems,  how- 
ever, the  outer  part  of  the  band  maybe  morphologically  secondary  cortex. 
This  circumstance  occurs  in  the  following  manner:  When  cork  is  formed, 
it  is  likely  to  take  its  origin  in  cells  exterior  to  the  chlorophyll  band  and 
very  close  to  it.  By  the  activity  of  the  phellogen  periderm  is  organized 
without  and  phelloderm  within  in  the  usual  fashion  and  in  the  cells  consti- 
tuting the  phelloderm  chlorophyll  may  be  found.  Consequently  it  happens 
that  in  older  stems  of  certain  plants,  as  in  Celtis  pallida,  fig.  3,  the  outer 
portion  of  the  chlorophyll  band,  in  addition  to  being  of  different  origin,  may 
be  more  recently  organized  than  the  inner  portion.  There  appears  to  be 
a  limit  to  the  thickness  of  the  chlorophyll  band  brought  about  by  this 
means,  however,  as  the  portion  of  the  band  which  is  of  secondary  origin 
has  never  been  seen  to  be  more  extensive  than  the  primitive  part. 

Another  point  which  has  to  do  with  the  structure  of  the  chlorophyll  band 
relates  to  the  similarity  in  some  cases  and  the  dissimilarity  in  others  of 
the  structure  of  the  band  in  the  stems  and  the  structure  of  the  chlorenchyma 
of  the  leaves  of  the  same  plant.  In  all  plants  studied  palisade  tissue  of 
some  sort  was  foimd  in  the  leaves,  but  in  part  only  of  the  plants  was  the 


SPECIAL    STRUCTURAL    FEATURES.  35 

chlorophyll  band  of  the  stems  also  palisade — it  was  freciuently  spongy 
tissue.*  There  is  a  relation  between  the  structure  of  the  chlorenchyma  of 
the  stem  and  the  foliar  habit  of  the  plant  which  holds  in  all  well-marked 
cases  and  which  comparative  studies  on  the  forms  and  their  relatives  may 
show  to  be  valid  in  cases  now  not  so  clear.  The  relation  may  be  stated 
thus:  In  perennials  with  no  leaves,  or  with  rudimentary  leaves,  the  chloro- 
phyll band  of  the  cortex  is  structurally  palisade  tissue.  On  the  other  hand, 
perennials  with  relatively  large  leaves,  or  a  larg-e  leaf-surface,  have  chloro- 
phyll bands  of  spongy  tissue.  The  following-named  plants  either  have  no 
leaves  at  any  time  of  the  year  (in  mature  stage)  or  the  leaves  are  clearly 
of  a  rudimentary  nature  and  the  chlorenchyma  of  the  cortex  is  uniformly 
palisade:  Aster  spinosus,  Baccharis  cntoryi.  liplicdra  aiifisvp/iililica ,  Ka'bcr- 
linia  spinosa;  although  different  in  certain  regards  the  outer  part  of  the 
chlorenchyma  of  Cereiis  may  also  be  said  t(j  be  palisade.  On  the  other 
hand,  the  following  plants  have  a  pronounced  leaf-surface  and  the  chloren- 
chyma is  spongy  tissue:  Condalia  spathiilaca,  Covillea  fridriifafa,  Fonquicria 
splendens,  Parkiusonia  aculcata,  P.  torrcyana,  Salix  nigra,  Sanibucus  incxi- 
cana.  The  leaves  of  K'raiiiiria  cainscriis  should  probably  be  considered 
rudimentary,  although  of  fairly  large  size;  during  the  driest  seasons  the  plant 
is  leafless.  The  chlorenchyma  of  the  stem  is  palisade.  Zizyphus  parryi 
has  a  larg-e  leaf-surface  and  the  leaves  are  not  unlike  those  of  Fouqiiieria; 
like  Krameria,  the  leaves  are  usually  absent  during  dry  times.  The  chloro- 
phyll band  is  palisade.  Parkiusonia  microphylla,  as  the  specific  name 
indicates,  has  very  small  leaves,  so  small  that  their  presence  is  hardly  noted, 
and  yet  the  chlorenchyma  of  the  stem  is  of  spongy  tissue.  It  should  be 
said  also  that  the  leaves  of  P.  microphylla,  as  well  as  those  of  the  most  leafy 
forms,  fall  away  with  the  advent  of  dry  seasons. 

Whatever  may  be  the  significance  of  this  variation  in  structure  of  chlor- 
enchyma of  stems  of  perennials,  there  appears  to  be  a  fairlv  uniform  relation 
between  it  and  the  character  of  the  tissues  exterior  to  the  band.  The 
exceptions  to  this  relation  are  at  least  no  more  striking  than  the  exceptions 
to  the  relation  of  structure  and  leaf -habit  gfiven  above.  The  relations  have 
to  do  especially  with  the  depth  of  the  chlorophyll  band,  the  presence  or  the 
absence  of  pig-ment  in  the  exterior  tissues,  and  perhaps  also  with  the 
presence  or  absence  of  trichomes. 

As  a  rule,  the  depth  of  the  chlorophyll  band  may  vary  with  the  age  of 
the  stem;  however,  in  young  stems,  e.  g.,  those  about  1  cm.  in  diameter, 
there  is  much  constancy  in  this  regard.  Aster  spinosns,  Baccharis  enioryi, 
and  Kramer ia  canes cens,  all  of  which  must  be  considered  plants  with  a 
reduced  transpiring  surface,  have  the  following  depths  of  the  chlorophyll 
band:   19.2  /*,  16  /*,  18.8  /*,  respectively.     These  forms  have  paHsade  chlor- 


*The  leaves  of  Opuntia  versicolor,  and  perhaps  of  other  opuntias,  do  not  appear  to 
have  palisade  tissue,  although  palisade-like  tissue  is  to  be  found  in  the  permanent  parts, 
namely,  the  stems.  Compare  fig.  14,  Biological  Relations  of  Certain  Cacti,  W.  A.  Cannon, 
American  Naturalist,  1906,  40  :  27. 


36         TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IX  DESKRT  PLANTS. 

enchyma  in  the  stem.  With  its  cxtrcmclx'  thick  cuticle,  80  m,  K'a-bcr/iiiia 
is  a  marked  exception  to  this  ecjndition.  Contrast  the  dejjthof  the  band  as 
given  for  these  species  with  that  of  the  stems  of  Celtis  pallida,  Covillea  triden- 
tata,  Parkinsonia — representing-  the  leafy  class  of  parennials.  The  figures 
are  96  M,  48  M,  and  83  M,  respectively.  All  of  these  forms  have  spongy 
chlorenchj'ma  in  the  stem. 

There  is  also  fair  consonance  between  the  kind  of  chl()reneh\-ma  and  the 
kind  of  tissue  exterior  to  it.  In  Aster,  Baccharis,  Kramcria,  Kivbcrlinia, 
Ceretis — plants  with  a  reduced  leaf-surface  or  with  no  leaves — the  chlorophyll 
band  extends  to  the  epidermis.  vSuch  is  the  condition  to  be  met,  not  alone 
in  young,  btit  also  in  old  stems  of  these  plants,  which,  however,  is  not  the 
final  condition  in  most  of  them.  In  the  type  of  plants  with  larger  leaves, 
or  larger  leaf-surface,  on  the  other  hand,  there  is  frequently  when  young, 
and  always  when  old,  some  sort  of  tissue,  in  addition  to  the  epidermis,  which 
serves  as  a  covering  to  the  chlorophyll  band.  This  may  be  hypodermal 
tissue,  cork  in  most  plants,  or  in  Olneya  a  curious  proliferation  of  the  epi- 
dermal cells  in  the  young  branches  by  which  a  many-layered  ei)idermis  is 
organized.  It  will  be  recalled  that  in  the  former  class  of  perennials  the 
chlorenchyma  is  palisade  and  in  the  latter  spongy  tissue. 

In  yet  another  structural  characteristic  the  two  classes  of  plants  are  dis- 
tinguished. With  certain  exceptions  plants  with  rudimentary  leaves  or  none 
have  no  pigment  in  the  epidermis,  i.  e.,  the  parts  exterior  to  the  chlorophyll 
band  are  colorless.  But  in  Celtis,  Condalia,  Olneya,  and  Prosopis  all  forms 
possessing  a  pronounced  leaf-surface,  either  the  epidermis  or  the  hypoderm, 
or  again  the  periderm,  is  provided  with  a  pigment  which  is  usually  of  a 
dark-red  color.  In  these  forms  the  chlorenchyma  is  of  spongy  tissue.  An 
exception  to  this  is  found  in  Parkinsonia,  which  has  no  pigmented  tissues 
exterior  to  the  chlorophyll  band. 

The  coincidences  which  have  been  repeatedly  observed  of  spongy  chlor- 
enchyma and  pigmented  exterior  tissues  lead  to  the  belief  that  the  relation 
between  the  two  is  something  more  than  a  chance  association.  This  is 
strengthened  by  the  further  observation  that  in  palisade  chlorenchyma  no 
such  exterior  pigmented  cells  are  usually  to  be  found. 

Although  no  hard  and  fast  rule  can  be  given,  it  appears  that  perennials 
which  have  a  reduced  leaf-surface  present  the  following  characteristics 
regarding  the  chlorophyll  band  of  the  stem:  Its  structure  is  wholly  or  at 
least  in  i^art  palisade;  it  usuall\-  lies  close  to  the  surface,  and  the  tissues 
exterior  to  it  usually  do  not  contain  pigment.  While,  on  the  other  hand, 
perennials  with  a  pronounced  leaf-surface  possess  a  chlorophyll  band  of 
spongy  tissue,  there  is  usually  some  kind  of  tissue  in  addition  to  the  epider- 
mis between  it  and  the  surface,  and  the  exterior  tissue  usually  contains 
pigment. 


LIMITS    OF    CHLOROPHYLL    DISTRIBUTION.  37 

PENETRATION  OF  THE  CHLOROPHYLL. 

The  greatest  depth  at  which  chlorophyll  was  found  beneath  the  surface 
of  the  plants  varied  from  0.38  mm.  in  Kceberliniaspinosa  to  6.6  mm.  in  Cereus 
^igantcns .  In  ordinary  leaves  chlorophyll  occurs  from  0 . 04  mm .  to  0 . 3 5  mm . 
from  the  surface.  As  contrasted  with  the  depth  of  chlorophyll  in  leaves, 
that  in  the  stem  is,  therefore,  from  about  9  to  165,  or  0.5  to  18.8  times  more 
distant.  In  these  desert  plants,  of  a  conseciuence,  there  are  very  unusual 
conditions  to  which  the  chlorophyll  of  the  stems  may  be  subjected  and 
under  which  photosynthesis  ma>-  be  carried  on.  The  most  deeply  placed 
chloroi^hyll  probably  has  the  miniminn  amcnrnt  of  lig'ht,  or  the  minimum 
de.oTee  of  aeration,  or  the  least  amoimts  both  of  air  and  of  li.y'ht.  Adequate 
water-supply  as  well  as  suitable  temperature,  more  surely  the  latter,'''  are 
presupposed  to  exist. 

As  is  well  known,  chloroi^lastids  of  certain  plants  may  exercise  their 
function  of  carbon  assimilation  inider  exceedingly  feeble  illumination. 
Pfeffer  (Physiology  of  Plants,  Eng-.  ed.,  vol.  1,  p.  340)  states  that  photo- 
synthesis may  occur  at  an  illumination  1/600000  the  intensity  of  sunlight. 
It  is  not  surprising,  in  view  of  this,  in  a  region  where  light  is  so  intense  as 
in  the  desert,  that  we  find  chlorophyll  over  0.5  cm.  beneath  the  surface 
(in  extreme  instances  probably  much  deeper  than  this). 

The  light  tonus  probably  plays  an  important  role,  as  indicated  by  the  rang-e 
of  the  position  of  chlorophyll  in  the  stem.  This  condition  is  well  known 
in  plants  inhabiting  more  moist  regions.  Chloroplasts  of  many  plants 
become  pale  and  discolored  after  a  few  days  in  darkness.  The  paling  of 
grass  and  of  low  herbaceous  plants  in  weak  lig-ht  which  obtains  during:  a 
long  wet  season  are  familiar  examples  of  the  dependence  of  the  chloro- 
plastids  of  such  forms  on  a  constant  and  considerable  supply  of  lig-ht.  On 
the  other  hand,  plants  belonging  to  the  Caetaeese  and  Coniferae,  as  well  as 
Elodea,  CJiara,  etc.,  are  more  resistant  and  may  remain  green  for  a  month 
or  more  in  darkness.  But  the  fact  that  at  a  depth  of  6.6  mm.  the  chloro- 
plastids  of  Cerens  are  green  in  old  stems  is  indication  not  of  survival  but  of 
their  being  functional  at  the  moment.  It  is  not  known  what  the  maximum 
light  stimulus  may  be  that  the  chloroplastids  of  Cereics  may  endure  without 
injury,  but  Pfeffer  states  that  chloroplastids  of  Elodea  can  be  exposed  to 
light  more  intense  than  60  times  concentrated  sunlight  without  injury.  If 
a  comparison  of  the  life  conditions  of  Elodea  with  that  of  the  desert  forms 
is  permissible,  we  mig'ht  expect  the  chloroplastids  of  Cerens  and  of  other 
desert  types  to  be  exceedingly  resistant  to  light. 

The  considerable  extent  of  the  chlorophyll  apparatus  in  the  desert  ]:)lants 
emphasizes  another  condition  which  is  probably  not  present  in  leaves,  or  if 
so,  to  a  limited  extent  only,  namely,  what  majr  be  termed  the  light  stress 
which  the  protoplast  of  the  desert  plant  experiences.      The  outer  chloro- 

*Compare  distribution  of  chlorophyll  in  Parkniso/iia,  p.  23. 


38 


TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IX  DESERT  PLANTS. 


plastids  are  subject  to  an  unknown  but  hi.u'h  degree  of  insolation;  to  which 
the  innermost  ones  are  subject  to  an  unknown  but  exceedingfly  small  degree. 
Thus  there  is  experienced  at  the  same  moment  a  very  wide  range  in  the 
intensity  of  the  light  stimulus.  What  the  effect  on  the  morphology  of  the 
chlorenchyma,  especially,  of  this  lig-ht  stress  in  such  a  plant  as  Cereiis,  in 
which  the  chlorophyll-bearing:  tissues  endure  throughout  the  life  of  the 
plant,  perhaps  unchang-ed,  maybe,  has  not  been  inquired  into,  but  probably 
it  is  a  very  important  factor  to  be  reckoned  with  and  one  that  must  be  taken 
into  account  in  studies  on  this  general  subject. 

The  relation  of  the  deeply  seated  chloroplastids  in  the  stem  of  such  i)lants 
as  Cereus  or  Parkinsonia  to  air  is  very  different  from  such  relation  in  leaves, 
where  the  character  of  the  structure  insures  abundant  aeration.  To  a 
relatively  long  distance  from  the  source  of  supply  of  oxyg-en  and  carbon 
dioxide  and  small  intercellular  spaces  of  the  typical  xerophyte,  is  added 
immobility  of  stems,  so  that  g:aseous  exchange  between  the  external  atmos- 
phere and  that  inside  the  plant,  as  well  as  between  different  portions  of  the 
plant,  is  not  aided  by  various  bending's  and  movements  characteristic  of 
leaves.  This  may  result  in  a  condition  in  which  unusually  small  amounts 
of  air  reach  the  deeper  tissues,  so  for  this  reason  photosynthesis  is  precluded. 
Indeed,  the  manner  of  recession  of  the  chlorophyll  from  the  stem  sugg'ests 
that  poor  aeration  rather  than  the  lack  of  sufficient  light  may  be  an  impor- 
tant factor  in  limiting-  the  depth  at  which  chlorophyll  may  be  functional. 
It  will  be  recalled  that  in  Celtis  pallida,  as  well  as  in  other  forms,  the  wood 
parenchyma  which  surrounds  or  is  most  closely  related  to  the  larg-e  ducts 
retains  chlorophyll  after  it  has  disappeared  from  other  portions  of  the  woody 
cj'linder  as  far  removed  from  the  surface  or  even  considerably  nearer  the 
surface . 

Penetration  of  the  chlorophyll. 


Species. 

Diameter 
of  branch. 

Depth  of 
chloropliyll 

mm. 

8 

(?) 
1-5 

3o 

4 

6.6 

0.75 

Cereus  gigaiiteus 

Condalia  spathulaca 

3-5     1          0-38 
2.5               1.25 
5-5               2.75 

Olneva  tesota    

torrevtina      

" 

Pfeffer  states  (loc.  cit.,  p.  329)  that  enough  carbon  dioxide  may  be  taken 
up  by  the  roots,  when  transj^iration  is  active,  to  prevent  the  more  deeply 
seated  chloroplastids  at  the  base  of  the  stem  from  losing  the  power  of  assim- 


PENETRATION  OF  THE  CHLOROPLYLL.  39 

ilating-  carbon  dioxide  when  exposed  to  lig-ht  for  long-  periods  in  an  atmo- 
sphere free  from  this  gas.  In  Cerens,  however,  the  main  source  of  the  gas 
is  probably  through  the  stomata,  although,  as  in  Ce/tis  and  other  plants, 
the  roots  may  be  of  importance  as  organs  of  aeration  as  well. 

The  table  on  the  preceding  page  presents  the  greatest  observed  depths  to 
which  chlorophyll  penetrates  and  remains  green  in  the  stems  of  perennials. 
Considerable  care  was  exercised  in  selecting  material  and  the  estimates  in 
each  instance  are  probably  conservative. 

IMPORTANCE  OF  CHLOROPHYLL  BAND. 

As  has  been  already  discussed,  the  leading  chloroj^hyll -bearing  tissue  in 
the  stem  is  the  subepidermal  chlorenchyma,  which  in  this  paper  has  been 
designated  the  chlorophyll  band.  This  also  is  the  most  enduring  chlor- 
ophyll tissue  of  the  stem.  It  constitutes  practically  the  entire  carbon 
assimilative  apparatus  in  plants  with  reduced  transpiring  surface— a  very 
important  part  of  the  apparatus  in  deciduous  plants — as  it  does  the  entire 
apparatus,  or  nearly  so,  in  the  leafless  forms.  In  Baccharis,  Cereiis,  Fon- 
qiiieria,  Kceberlinia,  Krameria,  Parkinsonia,  and  Z/st/^//?/.?  it  exists  throiigh- 
out  the  life  of  the  plant;  in  markedly  leafy  plants  its  importance  is  less, 
perhaps,  but  still  that  it  is  of  gfreat  moment  in  their  economy  can  not  be 
doubted.  It  is  least  important  in  the  evergreen  forms,  as  Ce/tis  pallida  and 
Condalia  spathnlaca. 

The  chlorophjdl  band  has  been  identified  in  the  following  plants  at  the 
several  distances  given  from  the  tip,  which  are  not  supposed  to  represent 
the  maximum  distance  in  any  case,  but  may  do  so:  Celtis,  178  cm.;  Con- 
dalia, 95  cm.;  Covillea,  95  cm.;  Franseria,  15  cm.;  Olneya,  120  cm.;  Proso- 
pis,  123  cm.  The  relative  importance  of  the  band  appears  more  clearly, 
perhaps,  when  its  volume  in  several  plants  is  compared.  In  order  to  insti- 
tute the  comparison  the  diameter  of  stem  nearest  1  cm.  was  taken,  and  the 
measurement  of  the  chlorophyll  band  applied  directly  to  an  ideal  stem 
100  cm.  in  length  and  1  cm.  in  diameter.  In  this  manner  Celtis,  with  a 
chlorophyll  band  0.025  mm.  wide,  would  have  a  volume  of  0.098  cm.  in  a 
stem  100  cm.  in  length;  Kceberlinia,  0.415;  Parkinsonia  microphylla,  OA77; 
Prosopis,  0.578.  The  ratios  are,  approximately,  Celtis,  1;  Kwberlinia,  4.1; 
Parkinsonia,  4.7;  Prosopis,  5.7.  Of  these  plants  it  will  be  noted  that 
Kceberlinia  and  Parkinsonia  rely  mainly  or  wholly  on  the  chlorophyll  band 
for  their  carbon  assimilation  all  of  the  year  and  Prosopis  a  part  of  the  year, 
while  Celtis,  which  is  evergreen,  but  nevertheless  has  considerable  chloro- 
phyll in  its  stem,  depends  mainly  on  the  extensive  leaf-surface.  With 
Prosopis  should  be  classed  Olneya;  and  with  Celtis  should  be  classed  Covillea 
and  Condalia,  whose  evergreen  habit  makes  the  chloroi:)hyll  in  the  stem  of 
ess  importance  in  the  assimilative  processes. 


40         TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IN  DESERT  PLANTS. 
Measurements  on  the  chlorophyll  band. 


Species. 


Aster  spinosus 

Baccharis  emoryi 

Celtis  pallida 

Do 

Cereus  giganteiis 

Condalia  spathulaca 

Do 

Covillea  trideiitata 

Do 

FoLiquieria  splcndens 

Do 

Koeberlinia  spino.sa 

Do 

Kranie>-ia  canescens 

Do 

OIneya  tesota 

Do 

Parkinsonia  microphylJa. 

Do 

Do 

Parkinsonia  torreyana.... 

Do 

Prosopi.s  velutina 

Do 

Zizyphus  parryi 

Do 


niamPtPr  I    Width  Of        Depth  of 
o^h^Sir.  |cb.oroP^;yli;eh.o3hy,, 


25.6 
25.6 


144 
1 12 

83.2 
60.8 

160 
83 
130 
246 
144 
224 

3- 
160 
57-6 
64 


19.2 
16 

96 

108. S 

5«' 

80 

19.2 

48 

80 
498 
1 162 

80 

64 

18.8 

32 

38-4 

64 

83 
144 
130 

64 
128 

48 

32 

19.2 

41.6 


PERSISTENCE  OF  CHLOROPHYLL  IN  THE  WOODY  CYLINDER. 

Chlorophyll  in  the  woody  cylinder  is  a  striking-  characteristic  of  young- 
Pa:  r/^/?«<?w/rt  and  Prosopis  branches  especially,  and  is  found  in  nearly  all  Of 
the  other  desert  perennials.  Compared  to  the  chlorophj-ll  of  the  cortex, 
however,  it  is  likely  of  little  profit  to  the  plant,  for  the  reason  that  it 
disappears  early  from  the  stem.  How  long  it  persists  was  not  learned  in 
any  case,  since  the  plants  studied  did  not  exhibit  annual  rings,  or  in  any 
other  way  give  a  clue  as  to  the  rapidity  of  growth. 

The  subjoined  table  g'ives  the  character  of  the  branch  at  a  time  when 
the  chlorophyll  for  the  most  part  had  already  left  the  woody  c.\'linder.  The 
measurements  were  made  on  the  disappearance  of  chlorophyll. 


«ru.,.ioc                             Diameter 
^Pec'es.                         1  ot  branch. 

Distance 
from  tip. 

Remarks. 

mm. 
Celtis  pallida  10 

cm. 

144 
65 
35 
60 
40 

120 

No  chlorophyll  in  wood  or  pith. 

Do. 

Do. 
Sparingly  present  in  wood  and  pith 
No  chlorophyll  in  woody  cylinder. 

Do. 

Do. 
Sparingly  present  in  wood  and  pith 

Condallia  spathulaca 7-5 

Parkinsonia  microphylla 15 

torreyana 22.5 

SUMMARY   OF    RESULTS.  41 


SUMMARY. 


The  leading-  results  of  this  study  may  be  summarized  as  follows: 

1.  Young-  stems  of  desert  perennials  contain  chloro]3hyll  in  most  of  the 
parenchyma,  both  of  cortex  and  of  woody  cylinder.  The  most  important 
chlorophyll -bearing  tissue  appears  in  transverse  sections  of  the  stem  as  a 
band  in  the  outer  part  of  the  cortex. 

2.  The  epidermis  of  branches  of  Parkiiisoiiia  1  cm.  in  diameter  may 
contain  chlorophyll. 

3.  Chlorophyll  is  present  in  the  i)hell(xlcrm  of  the  following-  species: 
Cc/tis  pallida,  Condalia  spat/iulaca,  Olncya  tcsota. 

4.  There  is  no  chlorophyll  in  the  woody  c>'linder  of  Aster  sf)i)iosits  or 
Baccharis  cincvvi . 

5.  The  woody  cylinder  in  young-  stems  of  Ephedra  antisyphilitica  and  of 
Olneya  tesota  do  not  contain  chlorophyll;  in  older  stems  the  woody  cylinder 
of  both  is  chlorophyllaceous. 

6.  The  chlorophyll  band  in  the  stems  of  Cereus,  Fouquicria,  I\)aiiicria, 
Parkiiisonia,  and  probably  also  in  Zizyphus,  persists  throug-hout  the  life  of 
the  member  bearing-  it.  In  most  plants  it. is  ultimately  cut  off  throug-h 
the  formation  of  cork. 

7.  As  reg-ards  foliar  habits  the  plants  studied  may  be  classified  into  two 
g-roups,  which,  however,  are  not  always  well  marked.  In  one  class  leaves 
are  either  rudimentary  or  wanting-;  in  the  other,  leaves  are  present  at  least 
during-  the  favorable  seasons,  /.  <?.,  when  the  water-supply  is  adequate  to 
their  needs. 

8.  The  differences  in  leaf-covering-  are  accompanied  by  fairly  consistent 
morpholog-ical  differences,  as  follows:  The  plants  with  reduced  leaf -surface, 
or  with  no  leaves,  have  palisade  chlorenchyma  in  the  cortex;  the  chloro- 
phyll band,  at  least  in  young- stems,  lies  near  the  surface;  the  tissues  exte- 
rior to  the  band  in  young-  and  generally  in  old  leaves  do  not  exhibit  pro- 
tective devices.  Plants  with  a  more  pronounced  leaf-surface,  on  the  other 
hand,  have  a  spong-y  chlorenchyma  in  the  cortex;  it  is  usually  more  deeply 
placed;  and  the  exterior  tissue  usually  has  some  protective  arrangements, 
as  pigmented  cells  or  a  hairy  covering. 

9.  The  greatest  depth  at  which  functional  chlorophyll  was  found  ranged 
from  0.38  mm.  in  I\ivhcrUiiia  spiiiosa  to  6.6  mm.  in  Cereiis giganteus.  This 
is  from  0.5  to  165  times  deeper  than  the  greatest  depth  of  chlorophyll  in 
ordinary  leaves. 

10.  The  depth  of  penetration  is  probably  limited  by  the  air-supply  rather 
than  the  supply  of  light. 

11.  The  chlorophyll  band  of  the  stem  constitutes  practically  the  sole 
engine  for  carbon  assimilation  in  Aster  spinosus,  Baccharis  emoryi,  Cere7is 
giganteus,  Kcvberlinia  spinosa,  Krameria  canescois,  and  the  most  important 


42         TOPOGRAPHY  OF  CHLOROPHYLL  APPARATUS  IN  DESERT  PLANTS. 

chloro]:>hyH  tissue  during'  the  most  of  the  year  in  Parkinsonia  and  Zizyphus 
Parryi. 

12.  The  volume  of  the  chlorophyll  band  for  a  unit  stem  has  a  value  of 
1  in  Celtis,  4.1  in  Ka-berlinia,  4.7  in  Parkinsonia,  and  5.7  in  Prosopis.  The 
least  volume  occurs  in  evergreen  forms;  the  greatest  in  plants  which  depend 
in  part  or  entirely  on  it  for  photosynthesis. 

13.  The  thickest  chlorophyll  band  is  in  Parkinsonia,  which  is  246  /^  in  a 
stem  4.9  cm.  in  diameter.  The  thinnest  band  is  in  Ccltis,  which  is  25  /*  in 
in  a  stem  1  cm.  in  diameter. 

14.  Chlorophyll  usually  disappears  early  from  the  woody  portion  of  the 
stem,  but  in  Parkinsonia  it  may  be  found  in  stems  1  cm.  in  diameter. 

15.  When  the  chlorophyll  band  is  palisade,  the  character  of  the  palisade 
is  ver\-  similar  to  that  of  the  leaf  of  the  same  plant. 

16.  The  following  species  were  studied:  Aster  spinosiis  Benth.,  Baccliaris 
emoryi  Gray,  Celtis  pallida  Torr.,  Cereics  giganteus  Englm.,  Condalia  spathu- 
laca  Gray,  Covillea  tridentata  Vail,  Ephedra  antisyphilitica  C.  A.  Meyer, 
Fouquieria  splendens  Englm.,  pyanseria  dumosa  Gray,  Krameria  canescens 
Gray,  Ka'berlinia  spinosa  Zucc  Olneya  tcsota  Gray,  Parkinsonia  aciileaia 
L.,  Parkinsonia  niicropliylla  Torr.,  Parkinsonia  torreyana  Watson,  Prosopis 
veliitina  Wooton,  Salix  nigra  ]\Iarsh,,  Sanibucus  mexicana  Presl.,  Zizyphus 
parryi  Torr. 


The  Induction,  Development,  and  Heritability 
of  Fasciations. 


BY 


ALICE  ADELAIDE  KNOX. 


Knox 


Plate     I 


OENOTHERA   PARVl  FLORA.     Fasciation  of  the   m^ 
of  the  side  branches. 


ith  n,ci|. 


THE  INDUCTION,  DEVELOPMENT,  AND  HERITABILITY  OF  FASCIATIONS. 


By  Alice  Adelaide  Knox. 


The  definition  of  fasciation  given  by  the  earher  writers  includes  plants 
with  axes  which,  normally  round  or  polyf^-onal,  have  become  flat,  and 
which,  wholly  or  in  part,  develop  through  a  linear  instead  of  a  cone-shaped 
growing-  region.  Such  stems  are  commonl}^  referred  to  as  banded  or  ribbon- 
shaped;  they  produce  abnormal  numbers  of  leaves  and  flowers;  they  possess 
an  altered  phyllotaxy;  and  they  usually  show  bifurcations,  or  splitting-s, 
somewhere  throug'h  their  leng-th.  The  last  tendency  is  so  marked  that 
fasciation  may  be  said  to  include  two  tendencies — one  toward  the  enlarg-e- 
ment  and  another  toward  the  division  of  the  axes  affected. 

Ring-fasciations  have  circular  growing-  reg-ions ,  and  the  upper  part  of  the 
stem  is  shaped  like  a  funnel  with  a  cavity  continually  wider  toward  the  top. 
The  funnel  commonly  breaks  on  the  side,  and  the  stem  finally  becomes 
flat;  for  this  reason  they,  too,  come  under  the  head  of  the  banded  forms. 
The  various  torsions  of  stems  of  this  character  described  by  Godron  (4),* 
Masters  (3),  and  others,  seem  to  be  caused  by  inequalities  of  growth  result- 
ing- from  injuries  on  the  concave  side.  The  fact  that  the  curves  may  b.e 
caused  by  injury  is  referred  to  by  Nestler  (7)  for  Sambucus  nigra  and  So?i- 
c/ius  palustris,  and  will  not  be  especially  noted  in  this  paper.  Plate  i,  and 
plate  II,  figs.  1  and  3,  give  an  adequate  idea  of  the  vertical  development  of 
fasciated  axes .  The  material  for  the  research  presented  was  gath-ered  from 
the  Oenotheras  of  Dr.  D.  T.  MacDougal's  experimental  ground  at  the  New 
York  Botanical  Garden  and  from  the  plants  of  a  waste  field  of  O.  bie finis 
in  Bedford  Park,  New  York  City.  Many  years  ago  Knight,  (l)  advocated 
enrichment  of  the  soil  for  the  culture  of  cockscombs,  and  de  Vries  also 
has  repeatedly  em])hasized  the  necessity  of  plenty  of  fertilizer.  The  experi- 
mental garden  provided  the  requisite  conditions,  but  although  fasciations 
were  more  abundant  in  the  rich  ground  their  prolific  production  on  plants 
that  grew  wild  in  the  sandy  waste  land  illustrated  the  force  of  de  Vries 's 
further  conclusion  (19)  that  the  innate  character  of  the  plant  is  more 
important  than  the  environmental  factors,  significant  as  he  deems  these 
to  be. 

The  life-cycle  of  biennial  primroses  divides  itself  into  (a)  the  rosette  stage, 
and  (^)"the  adult  stage,  when  the  flowering  stalks  develop  and  fruit.  -  The 

*The  figures  in  parenthesis  refer  to  the  bibliography,  page  i8. 


INDUCTION,   DEVELOPMENT,   AND  HERITABILITY  OF   !•  ASCIATIONS. 


Study  of  fasciation  is  naturally  i^-nniped  about  these  two  i^eriods.  The 
character  of  the  fasciated  rosette,  with  broad,  linear  heart,  .ii^ivino-  rise  to 
stems  flattened  from  the  base,  has  been  made  familiar  by  de  Vries  (11).  In 
the  cultures  such  rosettes  reached  a  breadth  of  3  cm.,  and  the  stalk  from 
one  of  them  produced  a  veg'ctative  line  which  eventually  measured  38  cm. 
(plate  i).  In  other  cases  the  first  evidence  of  fasciation  in  the  rosette  is  a 
bifurcation  of  the  .qrowins'  region,  and  two  tiny  buds  sometimes  appear  even 
between  the  cotjdedons.  The  two  types  of  rosettes  are  illustrated  by  plate  ii, 
fiS'.  4,  and  by  text-fig-.  1.     The  fasciation  of  the  flowering-  stalks  is  far  more 

common  than  that  of  the  rosette  and 
furnishes  the  bulk  of  the  material  for 
observation,  as  well  as  for  histological 
examination.  Usually  the  rosettes 
have  been  plants  to  be  kept  for  other 
experimental  purposes,  but  the  late 
branches   may  be   cut  at  will.     The 


Fig.  I. — Raiinannia  odorata,  bifurcated 
rosette. 


flowering  stems  studied  came  mostly 
from  two  sets  of  plants — the  wild 
O.  bioinis  and  the  O.  critciata  in  the 
garden.  There  were  man\-  ring- 
fasciations  in  the  two  groups,  though 
these  have  been  comparatively  infre- 
quently rei^orted.  The  O.  biennis, 
besides  simple  fasciations  and  ring- 
fasciations,  showed  on  many  stems, 
associated  with  the  banding,  an  indentation  or  groove,  as  represented  in 
plate  II,  fig.  2,  running  up  the  upper  half  of  the  stem.  The  groove  became 
wider  and  deeper  as  the  stem  flattened .  Simple  fasciations ,  ring-f asciati(ms . 
and  groove-fasciations  occurred  together,  both  on  secondary  and  tertiary 
branches  of  plants  of  which  the  main  axis  had  usually  been  stunted.  Two 
descriptions  may  be  taken  as  representative: 

Plant  1.-  The  plant  had  ii  branches,  which  were  all  equal  in  importance,  the  main 
tip  having  been  stunted  early  in  its  history.  There  was  consequently  no  main  branch, 
though  A  was  the  largest  secondary  branch.  The  tip  of  A  was  also  stunted,  and  it  had 
1 1  tertiary  branches;  of  these,  7  were  fasciated.  The  fasciations  were  split  into  two  or  more 
forks.  Two  of  them  showed  round  instead  of  flat  divisions.  In  six  cases  below  the 
bifurcations  there  were  grooves.  The  secondary  branch  B  was  also  fasciated,  with  a  flat 
tip.  The  flattening  was  in  every  case  associated  with  old  capsules,  often  with  holes 
bored  through. 

Plant  2.— The  plant  had  9  branches.  The  branch  A  had  6  secondary  branches,  all 
of  which  were  fasciated.  Two  of  them  showed  ring-fasciations,  the  others  were  flat,  and 
two  exhibited  conspicuous  grooves.  Of  the  other  branches,  one  showed  a  ring-fasciation 
and  the  others  bifurcations  and  simple  fasciations;  5  of  them  showed  grooves  so  as  to 


be  recognizable.     All  of  the  main  branches  were  fasciated. 
ciations  on  the  plant  was  15, 


The  total  number  of  fas- 


INDUCTION,   DEVELOPMENT,  AND  HERITABILITY  OF  FASCIATIONS.  5 

There  were  also  in  the  field  three  or  four  examples  of  the  type  in  which 
the  alteration  of  form  dated  from  the  rosette  stage.  These  individuals 
were  always  stalwart  plants  and  produced  high,  strong  stems,  of  which  the 
main  axis  was  fasciated  from  the  base. 

In  the  O.  cm  data  the  fasciations  were  remarkably  well  formed.  vSomc 
of  them  dated  in  their  development  from  the  rosette  period,  though  usually 
the  branches  did  not  begin  to  flatten  until  20  cm.  above  the  base.  Many 
of  them  suddenly  flattened  from  the  time  of  the  appearance  on  the  stem  of 
a  hard  protuberance,  which  was  usually  cylindrical  in  shape  and  sometimes 
2.5  cm.  in  length,  but  often  reduced  to  a  small  lump  on  the  stem  (plate  iii, 
figs.  1,  3,  4,  5).  Ordinarily  the  stem  fasciated  from  the  point  where  the 
protuberance  appeared  and  one  or  several  of  the  forks  were  fasciated.  If 
there  were  no  forks  the  whole  stem  at  once  banded.  There  were  also  ring- 
fasciations,  and  the  three  forms  appeared  on  the  same  plant. 
The  description  of  a  typical  individual  is  as  follows: 

C.  ().  2.— The  plant  developed  from  a  rosette  which  had  been  kept  in  a  cold-frame 
from  the  previous  fall  (1904),  and  most  of  the  branches  showed  by  the  early  disarrange- 
ment of  the  phyllotaxy  and  by  the  shape  of  the  stem  that  the  fasciation  had  started 
daring  the  rosette  period.  There  were  in  all  10  branches,  of  which  i  was  normal;  2  at 
theendof  the  second  summer  were  small  fasciated  rosettes;  7  were  repeatedly  bifurcated, 
3  of  them  eventually  into  9  forks.  Of  these,  3  showed  protuberances  at  the  point  of 
the  first  bifurcation.  One  stem  had  a  heavy  callus  at  its  base,  covering  an  old  injury. 
In  these  1905  plants  there  were  no  rings,  but  they  appeared  in  rgofi  on  stock  from  the  1905 
seed.  The  largest  fasciation  on  the  above  plant  measured  4.8  cm.  by  4  mm.  There  was 
frequently  a  constriction  or  channel  in  the  stem  below,  such  as  appears  in  the  plant  in 
plate  II,  fig.  I,  but  not  such  as  to  be  histologically  akin  to  the  grooves  in  the  wild  O. 
biennis. 

In  the  cruciate  forms  of  1905,  on  one  plant  15  out  of  16  branches  were 
fasciated;  on  another,  10  out  of  11.  For  the  microscopic  study  of  this 
material  there  were  to  be  examined  simple  flat  fasciations,  ring-fasciations, 
groove-fasciations,  and  the  fasciations  associated  with  the  protuberances. 

In  normal  structure  stems  of  Onagraceae  are  much  alike,  and  it  is  unnec- 
essary to  call  attention  to  small  differences.  They  possess  a  continuous 
bundle-ring,  which  is  bicollateral  in  character.  The  medullary  phloem  is 
arranged  in  groups  just  within  and  following  the  line  of  the  xylem.  The 
outer  phloem  is  in  very  sm'all  and  inconspicuous  groups  amid  a  ciuantit>'  of 
parenchyma  cells.  There  is  a  stereome  ring,  and  peripheral  to  this  chloren- 
chyma  several  rows  of  collenchyma  and  the  epidermis.  The  medullary 
rays  are  but  1  cell  in  width.  The  pith  consists  of  large  parenchyma  cells, 
and  there  are  many  bundles  of  raphides  of  calcium  oxalate  there  and  in 
the  cortex. 

There  is  a  kind  of  latex  system  which  consists  of  parenchyma  cells 
which  contain  a  brown  secretion,  most  dense  near  the  phloem,  but  con- 
spicuous in  pith,  cortex,  and  epidermis.  Sections  stained  in  Delafield's 
haematoxylin  resulted  in  a  bright  purple  in  the  cells  about  to  crystallize, 
in  brown  or  a  greenish  shade  in  the  latex  cells,  and  in  a  reddish  purple 


6  INDUCTION,   DEVKLOPMKNT,   AND  HERITABILITY  OF  FASCIATIONS. 

or  maroon  color  in  the  secretory  cells  of  the  i)arts  exposed  to  injury. 
Simple  fasciations  when  sectioned  show  the  traditional  structure  of  Hat 
stems  and  do  not  vary  from  the  normal  except  in  outline. 

Sections  of  ringf-fasciations,  as  diagTammed  in  plate  iv,  series  3,  follow 
closely  the  descrii^tion  of  Ncstler  (8)  for  l^erouica  longifolia  in  ha\'ing", 
besides  the  primary  bundle-rini^-,  a  second  bundle-rin.i^-  borderini^-  tlie 
cavity  of  the  funnel.  This  ring-  originates  as  a  group  of  meristematic  cells 
in  the  center  of  the  medullary  parenchyma.  Gradually  successive  gfroiips 
of  meristem  appear,  arranged  in  a  circle,  and  these  differentiate  into  tyi-)ical 
bicollateral  bundle-gnnips.  The  earliest  group  consists  of  several  undif- 
ferentiated cells,  which  show  their  first  tracheae  some  sections  above  their 
initial  appearance.  The  latter  g-roups  in  their  earliest  stag-e  consist  of  2 
cells  side  by  side,  a  trachea  and  a  nucleated  prosenchymatic  cell.  The 
parenchyma  cells  in  the  center  of  the  pith  below  the  first  signs  of  the  ring- 
are  smaller  than  the  peripheral  cells  and  more  crowded  together.  The 
phyllotaxy  of  the  stem  is  already  changed  from  the  normal  below  this  point , 
so  that  the  loss  of  definite  arrangement  is  seen  to  precede  the  formation 
of  the  meristems.  The  secondary  bundle-g-roups  gradually  increase  in  size 
and  merge  together  into  the  ring-;  there  appears  in  the  center  of  the  pith  a 
lysig-enous  cavity,  which  is  the  beginning-  of  the  hollow  of  the  funnel,  and 
further  differentiation  produces  an  internal  epidermis,  cortex,  and  stereome 
ring,  in  sequence  the  exact  reverse  of  the  primary  arrangement  in  the 
periphery.  At  the  apex  the  two  bundle-rings  merge  into  one.  When  the 
side  of  the  funnel  breaks,  the  two  rings  unite  at  the  break  and  surround 
the  elliptical  pith  of  a  simple  flat  fasciation.  As  there  are  leaves  and  flowers 
within  as  well  as  without  the  funnel,  there  are  leaves  and  flowers  on  both 
sides  of  the  banded  stem. 

The  structure  of  the  g-roove  fasciation  of  the  wild  O.  biennis,  shown  in 
plate  IV,  series  1,  presents  a  case  analogous  to  this.  At  an  early  stage  of 
development  a  portion  of  the  cambium  is  destroyed,  the  bundle-ring-  broken 
through,  and  the  space  is  filled  with  parenchyma.  The  expansion  and 
increase  of  the  undisturbed  cells  results  in  the  constriction  g,  which  is 
the  external  sign  of  the  groove.  In  the  interstice  in  the  ring  a  meristem 
develops  in  the  parenchyma,  succeeded  by  other  meristems  lateral  to  it. 
These  differentiate  into  a  line  of  bundle-groups  which  merge  with  each 
other  and  with  the  primary  ring.  During  this  process  the  stem  flattens, 
although  it  is  circular  when  the  meristem  appears.  The  flattening  is  a 
slow  and  at  first  imperceptible  process,  and  the  beg-inning-  of  the  alteration 
must  be  sought  far  below  the  point  where  it  is  visible  to  the  naked  eye. 
The  distance  of  the  open  groove  from  the  tip  is  17  to  26  cm.;  the  stems  are 
flat  and  broad  12  to  19  cm.  from  the  tip;  the  meristem  begins  from  2  to 
4  cm.  belowthe  opening- of  the  groove.  The  early  stages  of  the  process  may  be 
followed  by  a  reference  to  plate  v,  figs.  1  to  3.     Tlie  origin  of  the  meristem 


INDUCTION,   DEVELOPMENT,   AND  HERITABILITY  OF  FASCIATIONS.  7 

is  represented  in  fig.  1;  a  later  stage  in  fig-.  2  shows  the  character  of  the 
meristematic  groups  embedded  in  thick-walled  parenchyma,  and  in  fig.  3 
the  gradual  differentiation  into  phloem  and  xylem  is  pictured.  Interme- 
diate between  the  ring  and  the  groove  t\'pes  is  found  an  example  illustrated 
in  plate  iv,  series  4,  of  what  is  classed  by  Nestler  (8)  in  J\  longifolia  as 
an  "imperfect  ring."  In  this  the  meristems  arise  in  the  i^ith,  a  ring  of 
bundles  develops  there,  and  the  ring  passes  over  to  one  side  until  it  touches 
the  primary  bundle-ring,  with  which  it  then  fuses.  At  this  point  the  flat- 
tening of  the  stem  first  becomes  marked.  In  one  individual  the  lysigenous 
cavity,  characteristic  of  the  ring-fasciations,  formed  within  the  second 
bundle-ring  and  passed  out  into  the  cortex  when  the  two  bundle-rings 
merged.  Stems  with  the  protuberances  on  the  plants  of  O.  cruciata  when 
sectioned  (plate  iv,  series  2)  reveal  conditions  similar  to  those  of  the  two 
types  preceding.  The  medullary  parenchyma  cells  in  the  center  of  the 
stem  become  smaller  and  more  closely  crowded  together.  A  meristem  then 
arises  in  the  pith  and,  after  differentiating  into  a  secondary  bundle-ring, 
becomes  part  of  the  primary  ring,  as  in  the  intermediate  or  ring-groove 
type.  The  composite  ring  then  bulges  out  at  the  point  of  fusion,  and  a 
portion  of  it  is  cut  off  to  form  the  protuberance.  This  cylindrical  process 
(plate  V,  fig.  4)  possesses  a  woody  bundle-ring,  but  there  is  no  apical 
meristem  and,  near  the  tip,  primary  tracheae  and  sieve-tubes  run  irregularly 
across  its  axis  (plate  v,  fig.  6).  Above  this  are  irregular,  yellowish  callus 
cells  (plate  v,  fig.  5).  In  a  very  common  variant  of  its  structure,  serial 
sections  show,  in  the  pith  below  the  protuberance,  a  group  of  cells  formed 
of  tracheae  and  sieve-tubes,  which  run  transversely  and  in  great  confusion. 
As  this  group  passes  toward  the  periphery  and  touches  the  primary  bundle - 
ring  the  regularity  of  arrangement  is  disturbed  in  the  latter,  and  is  only 
restored  after  the  knob  has  been  entirely  cut  off  from  the  stem.  In  another 
variant  the  meristem  does  not  appear  below  the  protuberance,  nor  does 
the  stem  fasciate.  In  a  case  of  this  kind  the  cortex  around  the  main  stem 
was  found  to  be  eaten  off  by  insects,  the  growing  region  injured,  and  the 
lower  buds  forced  out.  This  is  simple  abortion  of  the  main  axis,  with 
destruction  of  leaves  and  buds,  which  leaves  the  surface  of  the  aborted 
stem  in  the  form  of  a  hard  and  smooth  projection.  The  variations  of  these 
regions,  of  which  there  may  be  said  to  be  almost  as  many  as  there  are 
specimens,  together  with  the  variations  of  the  rings  and  grooves,  are  all 
manifestations  of  the  same  principle.  The  early  conditions  of  one  are 
doubtless  similar  to  the  conditions  of  all,  and  for  this  reason  special  interest 
attaches  itself  to  the  young  stages  of  any  of  them. 

A  young  protuberance  wath  accompanying  fasciation  was  found  in  a  stem 
of  O.  cruciata,  illustrated  in  plate  iii,  fig.  6,  which  was  cut  in  September 
from  one  of  three  slow-growing  plants  which  had  elongated  20  cm.  from 
the  rosette  stage.     The  phyllotaxy  was  disturbed  for  3  cm.,  and  the  leaves 


8  INDUCTION,    DEVELOPMENT,   AND  HERITABILITY  OF  FASCIATIONS. 

abnormally  crowded  for  1.5  cm.  Transverse  sections  of  a  o:rowin5>-  reg-ion 
revealed  callus  over  the  main  tip,  just  above  the  pith.  The  procambial 
strands  about  the  callus  seemed  unaffected  by  the  injury  to  the  apical 
meristem  and  were  continuini;'  tlK-ir  activit.w  Lon.yitudinal  sections  of 
a  second  ]ilant  (plate  v,  fig.  7)  showed  callus  at  the  tip  of  the  main 
axis  in  the  former  position  of  the  apical  cells.  Beneath  it  trache;e  and 
sieve-tubes  had  differentiated  and  ran  irre.yularly,  man\-  in  a  transverse 
direction,  across  the  apex.  A  section  of  this  stem  is  seen  in  plate  v,  fig".  8, 
and  shows  the  callus  and  the  apical  conditions.  The  slig-ht  depression 
under  the  callus  is  surroiuided  by  a  rin.q'-shaped  meristem  (i)late  v,  hi.;'.  7). 
The  tip  has  evidently  been  injured,  the  meristem  has  spread  in  a  circular 
direction,  and  has  become  distributed  as  a  ring-.  As  enlargement  takes 
place  in  the  tip  of  the  stem,  its  apex  will  project  as  a  protuberance  of  greater 
or  less  development,  showing-  transverse  bundle-elements  beneath  a  mass 
of  callus.  When  tinequal  growth  pushes  the  callus  to  one  side  the  ring- 
splits  and  the  stem  becomes  flattened.  The  origin  of  the  injury  which 
induced  callus  formation  is  to  be  found  in  the  surrounding-  plants.  In  20 
rosettes  of  0.  cruciata  next  these  individuals  larvae  were  feeding,  and  as 
the  leaves  of  one  of  the  three  in  question  were  freshly  eaten,  and  as  another 
contained  a  larva  within  the  stem  in  the  lower  part,  these  insects  were 
undoubtedly  the  agents  which  attacked  the  young  tips. 

The  relation  of  certain  insects  to  the  Oenotheras  is  known  to  be  a  constant 
one,  and  more  than  one  genus  is  recognized  as  parasitic  upon  them.  The 
forms  found  in  Bedford  Park  and  in  the  experimental  grounds  are  species 
of  Mompha,  a  tiny  grayish  moth  with  spotted  wings.  The  eg-g-s  are  laid 
in  the  leafy  tips  and,  later,  larvae  are  abundant  in  the  apices,  the  capsules, 
and  the  pith  of  stalwart  plants.  They  are  particularly  common  in  rosettes 
toward  the  latter  part  of  the  summer,  and  as  they  develop  many  bind 
together  the  leaves  to  form  a  shelter  and  feed  among  the  tender  tissues  in 
the  winter  and  again  in  the  very  early  summer.  Most  of  them  eat  only  young- 
leaves  and  never  reach  the  meristem;  many  devour  and  destroy  the  apical 
tissues;  while  still  others  irritate  or  injure  them.  They  are  found  not  only 
in  the  rosettes  that  come  from  seed,  but  in  those  which  form  in  late  summer 
at  the  ends  of  old  branches  to  carry  over  a  perennial  growth.  The  fasci- 
ated  rosettes  of  late  summer  frequentl}^  appear  in  pairs,  and  it  is  common 
to  find  callus  and  inhibition  of  growth  between  the  two  (plate  v,  fig.  9). 
The  condition  of  the  branch  seems  to  indicate  that  the  main  axis  has  been 
destroyed  and  the  side-buds  injured  as  they  were  forced  out .  Such  branches 
commonly  have  circular  meristems  in  the  pith,  surrounding  spots  of  brown 
discoloration  of  the  sort  which  develop  about  masses  of  dead  cells. 

A  second  kind  of  injury  may  arise  through  the  ovipositors  of  the  insects. 
In  the  pith  of  Woody  stems  of  O.  cruciata,  O.  parviflora,  and  O.  bieyiriis,  and 
in  the  capsules  of  O.  grandiflora  and  other  forms,  are  larvae  closely  related 
to  those  in  the  rosettes.      Those  which  undergo  metamorphosis  in  the 


Knox 


Plate    II 


I.  — OENOTHERA  HYBRID.      Fasciations  developed  from  a  bifurcated  rosette. 
2.— OENOTHERA   BIENNIS.     Grooved  stem  with  fasciation  above. 
3.— OENOTHERA  CRUCIATA.     Ring  fasciation. 
4.— OENOTHERA   BIENNIS.     Fasciated  rosette. 

(See  also  text  figure.) 


INDUCTION,   DEVELOPMENT,   AND  HERITABILITY  OF  FASCIATIONS.  9 

capsules  of  O.  grandiflora  are  Mompha  brevhntclla,  known  at  one  time  as 
Laverna  cenot/iercevorella,  and  in  May  and  ag-ain  in  July  the  insects  are 
constantly  invading-  the  tips .  The  slightest  irregularity  in  the  arrangement 
of  the  young  leaves  during  or  just  preceding  the  flowering  period,  an 
appearance  like  that  shown  in  plate  iii,  fig.  2,  or  such  as  might  result  from 
some  external  mechanical  interference,  indicates  that  the  tip  when  sectioned 
will  prove  to  be  fasciated  or  bifurcated.  There  is  no  sign  externally  of  the 
fasciated  outline  in  these  tiny  tips,  merely  reddish  color,  inequality  of 
development,  or  a  tiny  aperture  suggesting  a  callus.  Microscopical  exam- 
ination proves  rin.g-fasciations  and  protuberances  to  be  abundant,  and  simple 
fasciations  occasional.  The  development  at  this  stage  covers  less  than 
5  mm.  of  the  stem,  but  is  none  the  less  perfect.  Two  such  apices  are 
diagrammed  in  plate  v,  figs.  10  and  13.  In  many  tips  are  found  long,  needle- 
like incisions,  illustrated  in  plate  v,  figs.  11,  12,  and  13,  as  if  made  by  an 
ovipositor.  About  these  the  cells  have  hypertrophied,  and  cylindrical  meri- 
stems  are  forming.  Throughout  the  stems  at  intervals  are  small  areas 
surrounded  by  hypertrophies  and  meristematic  conditions  (plate  v,  fig.  15). 
These  are  akin  morphologically  to  the  meristems  in  the  pith  of  the  old 
rosettes,  and  are  like  those  about  the  track  of  the  larvae  in  stems  in  which 
the  pith  is  infested  with  the  latter.  All  of  them  are  readily  recognizable 
because  of  the  pun^lish  intercellular  secretions,  seen  in  plate  v,  figs.  11, 
12,  14,  15,  and  the  changes  are  those  which  customarily  follow  in  the 
neighborhood  of  dead  cells.  Tips  of  this  appearance  collected  July  27, 
1906,  were  bifurcated,  if  not  definitely  fasciated;  none  of  them  were  normal; 
and  there  were  "stings"  of  various  sorts  in  them  all. 

The  anatomical  structure  of  rings  and  grooves  and  of  the  protuberances 
proves  them  to  be  variations  of  a  single  type,  for  the  essential  features  of 
their  development  are  the  same.  The  protuberance  varies  so  greatly  in 
its  structure  and  in  its  morphology  that  its  simplest  form  is  a  mere  callus 
associated  with  a  few  irregular  bundle-elements  projecting  from  the  side 
of  the  stem  (plate  iii,  fig.  4,  and  plate  v,  fig.  10,  k).  It  is  easy  to  conceive 
cases  in  which  the  injury  is  so  small  as  to  be  impossible  of  detection. 
Incisions  in  young  meristems  are  quickly  obliterated  by  the  turgidity  and 
growth  of  the  surrounding  cells  (plate  v,  fig.  12),  and  it  may  be  assumed 
that  many  fasciations  are  caused  by  injuries  too  delicate  to  follow  in  any 
but  the  initial  stages.  Only  chance  enables  one  to  find  such  stages,  and 
innumerable  tips  may  be  sectioned  without  avail.  To  a  stimulus  of  this 
nature,  obscure  in  its  histological  effects,  the  simple  fasciations  must  owe 
their  origin .  They  occur  on  the  same  plants  with  those  more  easily  detected , 
and  may  themselves,  when  bifurcated,  be  recognized  while  comparatively 
young.  Yet  the  stimulus  is  slow  to  produce  the  abnormal  condition,  and 
the  irritating  cause  is  concealed  before  the  effect  is  seen.  In  a  tip  of 
O.  biennis  which  contained  an  active  larva,  a  group  of  very  small  paren- 
chyma cells  had  differentiated  in  the   pith.     This   is  the  condition    that 


10         INDUCTION,   DEVELOPMENT,   AND  HERITACILITY  OF  FASCIATIONS. 

i:)recedes  a  rin,y;--fasciati()n,  thon.t^h  as  yet  no  ring--fasciation  was  apparent. 
In  all  wild  (\  diciniis  the  stems'were  infested  with  larvae  below  the  fasciations 
and  the  oTooves  full  of  eallus,  yet  it  was  impossible  to  find  intermediate 
conditions.  A  plant  with  a  fresh  larval  trail  up  the  side  fasciated  after  a 
month  of  elons'ation  from  the  rosette  sta.y-e,  but  by  the  time  the  character 
of  the  ti])  was  well  determined  the  first  eft'ects  were  obscured  by  the  later 
<4-rowth.  Unecpial  formation  of  wood  on  the  two  sides  at  the  base  of  fas- 
ciated stems  may  be  taken  as  an  indication  of  local  inhibiticjn.  Transverse 
sections  of  the  lower,  round  part  of  branches,  which  are  flat  above,  usually 
reveal  variations  in  the  width  of  the  woody  rin.^-.  The  difference  may  be 
slig-ht  or,  in  a  few  cases,  as  in  plate  v,  fig.  16,  very  marked  and  accom- 
i:)anied  by  callus  formation.  In  the  g:roove -fasciations  (plate  iv,  fi.Q's.  l/^ 
4/^)  the  width  of  the  primary  wood  where  it  adjoins  the  g-roove,  at  xx,  is 
narrower  than  at .rr.  This  is  also  found  to  be  true  in  sectioning-  the  rosettes 
cut  in  late  summer  from  the  old  stems  (plate  v,  fig".  9). 

What  has  been  said  applies  to  plants  out  of  doors.  It  seemed  probable 
that  a  different  state  of  thing-s  would  hold  in  the  gTcenhouse.  Yet  the 
fasciated  rosettes  in  the  greenhouse  have  in  the  stems  circular  meristems 
about  brownish  discolorations  and  a  sig-nificant  feature  of  their  development 
is  one-sidedness  of  growth  and  a  forcing-  out  of  the  axillary  branches. 
Rosettes  of  O.  crnciata  planted  June  16,  1906,  and  kept  in  the  g-reenhouse 
during-  the  summer,  were  subject  to  such  conditions  in  the  pith.  These, 
like  the  rosettes  of  O.  parviHora  of  1905-1906,  showed  roug'h  places  on  the 
l^etioles  and  midribs  of  the  leaves,  incurling-  of  some  of  the  leaves  in  the 
g-rowing-  tip,  and  ruffling-  of  the  margins.  The  O.  parviflora  planted  in 
the  summer  of  1905,  in  December,  showed  larger  and  longer  leaves. on  one 
side  than  on  the  other.  There  was  then  no  sign  of  linear  growth,  but  in 
April  they  began  to  fasciate,  and  in  May  all  four  plants  were  fasciated. 
Frequently  the  rosettes  tip  up,  owing  to  the  premature  development  of  a 
lateral  branch  (plate  ii,  fig.  4),  so  that  one  side  is  higher  than  the  other. 
This  looks  as  if  there  were  inhibition  of  growth  on  the  concave  surface. 
The  result  of  further  growth  is  often  a  complete  torsion  of  the  fasciated 
main  axis  with  fasciation  also  in  the  side  branches.  In  studying  fasciation, 
species  with  compact  symmetrical  rosettes  are  much  to  be  preferred.  O. 
irrandiflora  is  among  the  impracticable  forms,  for  the  side  branches  normally 
come  out  very  early.  A  double  rosette  of  Raimanuia  odorata,  a  near  relative 
of  the  Oenotheras,  the  plant  illustrated  in  text  fig.  1  and  in  plate  v,  fig.  17, 
when  sectioned  was  found  to  have  been  injured  below  the  bifurcation,  and 
at  this  point  (.vx)  there  was  inhibition  in  the  formation  of  wood.  Only  the 
bifurcated  fasciations  can  be  detected  at  the  start,  and  these  are  of  com- 
paratively rare  occurrence.  It  is  evident,  however,  that  the  rosettes  under 
cover  are  not  exempt  from  outside  injury,  and  insects  may  readily  enter  the 
greenhouse  through  the  ojK'n  ventilators,  besides  the  man\'  which  habituall>- 
live  there. 


INDUCTION,   DEVELOPMENT,   AND  HERITABIEITY  OF  FASCIATIONS.  11 

The  extensive  experiments  of  de  Vries,  which  have  led  him  to  consider 
certain  fasciations  hereditary  to  some  extent,  made  it  desirable  to  test  its 
inheritability  in  these  cnltures.  Pure  seed  was  saved  in  1905  from  fasciated 
plants  of  O.  criiciata,  and  of  O.  muricata  from  Kansas.  The  O.  cruciata 
came  from  material  ori.y-inally  collected  by  Mr.  S.  H.  Burnham  at  Lake 
Georg-e,  New  York,  in  1903.  Of  his  15  plants,  7  afterward  fasciated  in  the 
main  stem,  and  3  of  them  when  .qrown  i^rodnced  "curious  elbow-shaixxl 
structures"  on  the  stems.  These  protuberances  were  variants  of  those 
which  appeared  in  the  later  cultures.  Pure  seed  from  the  fasciated  indi- 
viduals was  sown  in  1904,  and  5  plants  saved  out.  These  fasciated  in  the 
main  and  side  branches,  and  from  them  pure  seed  was  sown  in  February, 
1906,  and  57  plants  saved  out.  In  September,  1906,  counting  the  main 
stems  only,  5  of  these  were  stunted  and  2  normal;  there  were  30  fasciations 
and  bifurcations  associated  wath  protuberances,  12  simple  bandings,  3  un- 
flattened  bifiircations ,  and  5  ring-fasciations.  In  the  normal  stock  plants 
there  were  in  one  group  of  3  individuals,  1  ring  and  2  bandings;  in  another 
of  4  plants,  2  protuberances,  1  bifurcation,  and  1  simple  fasciation;  a  third, 
of  4  individuals,  contained  some  fasciated  side -branches  on  each  plant.  The 
seed  of  the  <:^.  ^^ muricata''  was  sent  by  Mr.  H.  F.  Roberts  from  Manhattan , 
Kansas,  in  1904.  The  first  soAving  was  made  in  November,  1904.  Although 
distributed  as  '' muricata,' '■  it  proved  to  be  an  elementary  species  removed 
from  the  muricata  type.  Two  out  of  the  three  plants  saved  fasciated  in  the 
rosette  stage  and  bloomed  in  the  summer  of  1905.  From  one  of  these 
pure  seed  was  saved  and  sown  in  February,  1906.  In  September,  1906, 
out  of  43  plants,  26  individuals  w^ere  fasciated,  3  stunted,  2  bifurcated,  and 
12  apparently  normal.  Counting  only  the  flattened  tips,  60  per  cent  were 
fasciated.  In  the  3  control  plants  from  unfasciated  stock,  2  were  fasciated 
and  1  stunted.  The  control  in  each  case  fasciated  as  readily  as  did  the 
fasciation  cultures. 

Aside  from  the  series  which  were  run  as  special  tests  there  Averc  num- 
erous examples  of  fasciation  in  Dr.  MacDougal's  general  collection.  In 
1905  fasciation  was  found  in  55  individuals,  including  O.  lamarckiana,  O. 
muricata,  O.  biennis,  O.  oakesiana,  O.strigosa,  O.gigas,  O.  nanella,  O.grandi- 
flora,  O.  lamarckiana  X  O.  biennis,  and  O.  cruciata,  besides  many  forms  of 
doubtful  identity.  In  1906  it  appeared  in  86  individuals,  representing  34 
different  cultures  and  a  correspondingly  wide  range  of  species.  Next  to 
O.  cruciata,  O.  parvi/iora  fasciated  most  abundantl}'.  The  plants  were  in 
four  different  lots  from  Maine  and  in  one  lot  from  Madrid.  All  of  the 
individuals  fasciated  in  50  per  cent  of  their  branches.  Of  the  O.  grandi- 
flora  from  Alabama,  14  plants  were  fasciated.  In  the  O.  ammophila  all  5 
plants  were  fasciated  in  main  and  side  branches.  In  one  group  of  4  plants 
of  O.  lamarckiana,  from  a  parent  raised  after  a  succession  of  i:>ure  cultures 
from  seed  originally  sent  from  de  Vries  in  1901,  all  4  plants  were  fasciated 
in  the  main  stems.     The  anomaly  can  scarcely  be  considered  hereditary  in 


12  INDUCTION,   DEVELOPMENT,   AND  HERITABILITY  OF  FASCIATlONvS. 

all  of  these  forms,  s'athered  in  from  all  over  the  world,  nor  can  it  be  reg-arded 
as  the  sporadic  appearance  of  latent  characters.  The  fact  that  in  many 
series  from  normal  races,  100  per  cent  of  the  individuals  planted  out  fas- 
ciated,  though  no  selection  was  exercised  in  saving-  the  rosettes  from  the 
large  numbers  of  seedlings  origfinally  i^lanted,  strengthens  the  inference 
that  its  development  is  due  to  local  causes.  One  is  led  to  conclude  that 
there  have  been  prevalent  in  the  garden  and  in  this  region  during  the 
summers  of  1905  and  1906  swarms  of  insects  whose  attacks  upon  the  growing- 
tips  were  particularly  insidious  and  stimulative  without  being  at  the  same 
time  destructive.  It  happened,  too,  that  several  species  of  the  primroses 
were  rnarkedly  susceptible  to  the  injuries,  and  that  the  conditions  of  light 
and  nutriment  were  favorable  to  vigorous  development.  Given  similar 
conditions  of  culture,  the  factors  involved  in  the  production  of  the  fasciations 
are  the  specific  mode  of  attack  of  such  insects,  the  character  of  the  plant, 
and  the  rapidity  of  development;  the  second  of  the  three  is  the  most 
important,  as  it  is  true  that  in  two  adjacent  groups  of  O.  biennis,  one  will 
fasciate  and  the  other  will  not.  It  is  also  true  that  the  form  of  the  fascia- 
tion  varies  with  the  group  affected.  Thus  O.  '' muricata"  from  Kansas, 
O.  parviflora,  O.  ammophila,  and  O.  grandiflora  developed  simple-banded 
fasciations,  while  rings  and  protuberances  appeared  on  the  6>.  cruciata  and 
g-rooves  on  the  wild  O.  biennis.  The  O.  cruciata  from  the  Lake  George  stock 
differed  from  the  O.  cruciata  varia  if)  from  Hamburg-,  which  maybe  what 
de  Vries  calls  a  poor  race.  Of  this  O.  cruciata  varia  (f)  40  plants  sown  at  the 
same  time  with  the  Maine  cultures,  of  which  the  rosettes  were  bifurcated, 
failed  to  show  fasciation  either  in  the  rosettes  or  branches. 

This  grroup  of  plants  flowered  much  earlier  than  the  others,  which  calls 
attention  to  the  importance  of  the  late  development  of  the  individual.  Most 
of  the  fasciations  date  from  the  period  just  preceding  the  opening-  of  the 
flowers  in  July,  and  they  flatten  among- masses  of  fruits,  or  at  a  point  where 
the  stung-  flowers  have  fallen  off  and  left  the  stem  bare.  From  this  time  the 
eg-g-s  of  the  momphas  are  laid,  the  larvae  develop,  and  new  swarms  of  imag-os 
begin  to  emerg-e  toward  the  end  of  the  summer,  at  once  proceeding-  to  sting- 
new  tips.  Those  apices  which  have  passed  the  period  of  greatest  vig-or 
gradually  dwindle  away  and  die,  but  leafy  axes,  leafy  rosettes,  stems  ready 
to  flower  through  September,  all  soft  tissues  in  a  thriving-  condition,  then 
fasciate  in  greater  abundance  proportionately  than  earlier  in  the  season, 
for  their  limited  number  makes  it  more  certain  that  they  will  be  attacked 
by  the  recent- invasion  of  the  new  swarm.  In  the  rosette  stage  the  rate  of 
growth  is  also  important.  It  is  seldom  that  the  insect  reaches  the  apical 
meristem  of- a  quick-growing  plant,  for  the  rapid  formation  of  new  leaves 
supplies  sufficient  food  for  the  larva,  and  the  formative  region  remains 
imtouched.  Sections  of  numbers  of  young  ro.settes  containing  larvae  easily 
prove  that  the  insect  ordinarily  feeds  above  the  apex  or  at  its  side.  Though 
plants  are  often  unaftected  by  the  parasites,  doubtless  swarms  occasionally 


Knox 


Plate  III 


OENOTHERA  CRUCIATA,  I.  Young  protuberance.  2.  "Stung  tip."  3.  Old 
protuberance  and  bifurcation  with  one  fasciated  branch.  4.  Protuberances  asso- 
ciated with  the  flattening  of  the  stem.  5.  Protuberance  surrounded  by  fascia- 
tions.     6.  Early  stage  in  the  formation  of  a  protuberance. 


INDUCTION,   DEVELOPMENT,   AND  HERITABILITY  OF  FASCIATIONS.  13 

develop  whose  month-parts  are  sharper  than  those  of  their  fellows,  or  whose 
habit  it  is  to  bore  deep  for  the  young'est  and  most  tender  food.  In  the 
same  way  there  are  swarms  of  imag^os  which  have  longer  ovipositors,  or 
which  show  a  preference  for  the  center  of  the  apex  rather  than  the  axils  of 
the  embryonic  flowers.  If  the  character  of  the  attacks  of  the  insects  varies 
with  the  character  of  the  insect  swarm,  this  should  account  for  the  wide- 
spread appearance  of  fasciation  over  one  restricted  locality,  while  in  adja- 
cent areas,  beyond  but  insignificant  barriers,  no  fasciated  plants  are  found. 

The  "curious"  habit  of  fasciated  stems  in  that  those  of  annuals  are  at 
first  round  and  later  flatten,  while  those  of  biennials  originate  large  and  flat 
and  stay  so,  has  been  noted  by  de  Vries  (11 ).  In  the  primroses  under 
observation  this  seems  to  be  accounted  for  by  the  state  of  development  at 
the  time  of  the  sting  of  the  insect.  In  the  cultures  of  O.  parvifiora  rosettes 
planted  in  the  summer  of  1905,  and  kept  over,  fasciated  during  the  winter; 
those  sown  in  February  elongated  quickly  after  being  placed  out  and  fas- 
ciated in  the  upper  parts  of  the  branches.  Two  plants  of  the  February 
sowing,  which  g-rew  more  slowly  than  the  others,  were  fasciated  rosettes  in 
September.  In  general,  plants  or  branches  which  were  in  the  rosette  stage 
in  July  and  August,  or  at  the  time  when  the  insects  were  laying  their  eggs 
and  the  larvae  were  hatching,  fasciated  as  rosettes  and  produced  flat  stems 
the  following-  season.  Plants  in  the  flowering  state  during  the  same  period 
fasciated  in  the  upper  part  of  the  stems.  Plants  elongating-  from  the 
rosette  stage  in  September  fasciated  comparatively  low  down  on  the  stem  as 
in  plate  iii,  fig-.  6.  Any  plant,  moreover,  may  fasciate  in  its  rosette  stage 
the  first  season,  and  in  the  upper  part  of  its  side  branches  the  second 
season.  To  secure  the  most  striking  results  in  New  York,  seed  should  be 
planted  in  April  or  May  and  allowed  to  remain  out  of  doors  in  the  rosette 
stage  through  the  summer.  Plants  from  seed  sown  in  February  begin  to 
elongate  too  early  to  show  linear  growth  long  before  the  flowering-  tips  are 
ripe.  So  many  of  the  wild  plants  are  aborted  in  the  main  axis  that  one 
may  assume  that  the  tip  is  eaten  off  by  larvae  soon  after  the  plant  elongates 
from  the  rosette  stage.  Among  the  wild  plants  there  were  many  larva 
in  the  field  in  June  in  the  young  shoots.  The  side-branches  are  doubtless 
injured  as  they  are  forced  out,  for  the  callus  in  the  grooves  of  some  of  the 
branches  and  in  the  lower  parts  of  the  cavity  of  the  rings  in  others  indicates 
early  effects  of  injury  in  these  secondary  branches. 

The  conditions  of  culture,  as  has  been  already  stated,  were  favorable  to 
the  vigorous  growth  of  the  garden  plants.  Individuals  were  from  2  to  4 
feet  apart  and  were  well-fertilized  and  watered.  The  interesting  experi- 
ments of  de  Vries  and  of  Hus  (22)  at  the  Missouri  Botanical  Garden  sug-- 
gest  that  if  some  of  the  unfasciated  plants  had  been  subjected  to  different 
conditions  they  too  might  have  fasciated.  It  is  possible,  also,  that  if  the 
plants  had  been  planted  in  April  instead  of  in  Febniary  the  result  mig'ht 
have  been  different.     The  environment  must,  however,  be  suited  to  the 


14         INDUCTION,    DEVELOPMENT,   AND  HERITABILITV  OF  FASCIATION.S. 

individual  needs,  for  seed  from  the  fasciated  wild  O.  biennis  of  1905,  in  which 
the  tendency  toward  fasciation  was  so  marked,  when  sown  in  the  garden  in 
1906  produced  only  one  fasciation.  The  plants  of  this  group  flowered  very 
early,  however,  and  the  time  of  sowing-  maj-  have  been  as  important  a 
factor  as  the  change  of  environment,  or  even  more  so. 

That  fasciation  can  be  produced  by  mechanical  injur\-  has  been  known 
for  many  years,  and  Sachs  (6)  and  Goebel  (16)  both  treat  of  the  old  exper- 
iment where,  by  cutting  off  the  epicotyl  of  certain  germinating  seedlings, 
the  side-branches  forced  out  are  flattened.  Phaseolus  multiflorus  is  most 
commonly  used,  while  de  Vries  employed  Agrostemna  githago  (19).  Nas- 
turtiums also  respond  readily,  and  as  high  as  60  per  cent  of  fasciated 
individuals  was  obtained  in  one  water-culture.  The  injury  must  occur 
just  after  germination,  and  this  has  led  to  the  theory  that  the  anomaly 
is  caused  by  overplus  of  nutrition  rushing:  to  undeveloped  centers  of  growth 
(16).  The  effects  in  the  seedling-  are  not  lasting,  for  the  flattened  branches 
soon  revert  to  the  normal  shape.  It  is  possible  that  the  remoteness  of  the 
stimulus  from  the  meristems  affected  may  have  to  do  with  this.  In  the 
(jenotheras  the  injury  is  to  the  initial  meristem  itself,  and  is  of  a  nature  so 
delicate  that  no  relatively  coarse  instrument  can  duplicate  it  artificially. 
Repeated  attempts  were  made  to  induce  fasciation  in  the  primroses  with 
incisions  by  fine  sterilized  needles,  but  the  needles  either  destroyed  the 
apex  altogether,  in  which  case  the  side-branch  did  not  fasciate,  or  failed  to 
reach  it  at  all.  Any  incisions  that  could  be  made  were  so  destructive  com- 
pared with  those  of  the  sort  represented  in  plate  v,  fig.  13,  that  the  attempt 
was  finally  abandoned  altogether.  It  is  interesting  to  note,  in  support  of 
the  theory  of  the  influence  of  nutrition,  that  the  effects  in  the  Oenotheras 
come  during-  the  rosette  stage  and  just  before  flowering,  the  times  when  the 
elaborated  food  supply  is  mostabundantly  centered  at  the  g-ro wing  apex. 

The  discussion  of  the  nature  of  fasciation  has  centered  about  the  mor- 
phology of  the  enlarged  axis,  whether  it  is  the  enlargfement  of  a  single 
growing-  ])oint,  as  exemplified  by  Mouquin-Tandon  (2),  or  whether  it  is  the 
adnation  of  several  axes,  as  explained  by  Masters  (3).  After  a  careful 
histological  examination  of  fasciated  g-rowing-  tips  of  certain  Phanerogams 
and  Cryptog-ams,  Nestler  (7)  found  no  evidence  in  favor  of  congenital  adhe- 
sion. The  growing  line  gave  no  sign  of  complexes  of  growing  points,  but 
represented  an  enlarged  area  of  meristematic  cells.  In  the  Oenotheras  there 
has  never  been  any  evidence  in  favor  of  the  concrescence  theory.  In  one 
single  bifurcation  for  a  short  distance  the  epidermis  closed  around  two 
separate  axes,  but  this  was  accidental  grafting  of  two  separate  tips.  The 
phenomena  of  fasciation  are  phenomena  of  multiplication,  of  increase  in 
numbers  of  stems  and  leaves,  and  of  the  number  of  cells  which  enter  into 
their  composition.  Once  the  physiologfical  balance  of  the  growing-  cells  is 
changed  and  the  chemical  equilibrium  altered  by  the  peculiar  stimulus  of 
the  mechanical  contact,  the  tendency  to  multiply  develops,  and  frequently 


INDUCTION,   DEVELOPMENT,   AND  HERITABILITY  OF  FASCIATIONS.  15 

continues  to  the  end  of  the  life  of  the  plant.  If  there  were  fusion  of  a 
definite  number  of  growing'  regions  there  would  seem  to  be  a  definite  limit 
to  the  increase  in  the  size  of  the  stem  and  the  number  of  the  leaves.  Con- 
crcsence  may,  and  frequently  does,  occur  as  a  consequence  of  the  bifurca- 
tion which  is  so  intimately  associated  with  it,  but  is  an  accidental  rather 
than  an  essential  factor,  and  succeeds  rather  than  precedes  the  division  of 
the  axis.  As  to  the  reason  for  this  curious  alteration  of  form  in  these  fas- 
ciated  stems,  one  can  speak  only  theoretically.  It  may  be  that  the  banded 
fasciations  arise  from  lateral  injuries  in  which  the  inhibition  causes  the 
meristem  to  stretch  from  the  point  of  attack.  This  might  seem  to  be  illus- 
trated in  the  case  of  the  rosettes  of  one-sided  development  and  of  the  injured 
stems  plate  v,  figs.  9  and  16.  In  the  ring-fasciations  the  injury  may  be  to 
the  tip  of  the  growing-  meristem,  and  the  stresses  thereafter  distributed  in 
a  circular  fashion. 

Bifurcations  are  often  caused  mechanically  by  the  stresses  of  old  and 
broad  fasciations,  where  the  unequal  growth  and  the  consequent  torsions 
strain  the  large  growing  region  into  segments  through  virtue  of  its  unwieldy 
size.  It  is  to  be  expected  that  a  fasciation  such  as  that  in  plate  i  would 
soon  divide  in  this  way  if  allowed  to  grow  to  maturity.  The  splitting  of 
the  axes  may  be  more  frequently  mechanical  than  superficially  appears  to 
be  the  case.  We  must  suppose  that  in  its  early  stages  it  is  often  due  to 
the  stresses  of  vigorous  growth  in  an  abnormally  large  tip.  The  tensions 
which  are  parallel  with  the  vegetative  line  are  greater  than  those  which 
cross  it.  A  slight  disturbance  of  external  conditions,  and  so  of  the  growth, 
upsets  the  equilibrium,  and  the  tension  is  broken.  It  must  be  remembered, 
as  Nestler  has  shown  (7),  that  the  apex  is  not  level,  but  undulate,  and  it 
may  be  supposed  to  be  constantly  changing.  Certain  delicate  adjustments 
of  the  stresses  may  keep  the  equilibrium  until  alteration  in  the  rate  of 
growth,  due  to  inequalities  in  nutrition  over  so  extended  an  area,  upset  the 
balance  and  free  a  portion  of  the  axis.  In  the  smaller  segments  the  stresses 
are  not  so  great ;  consequently  there  is  increasing  tendency  toward  normal 
growth,  and  the  smallest  bifurcations  usually  in  the  end  completely  reverts 
to  it.  Bifurcations  sometimes,  both  in  ring-shaped  and  in  flat  fasciations, 
are  caused  by  injury,  but  in  many  cases  such  an  origin  can  not  be  assigned 
to  them. 

Though  the  development  of  fasciation  has  often  been  referred  to  external 
stimuli,  there  is  but  one  direct  reference  to  its  connection  with  insects. 
Molliard  (15)  in  1900  found  the  larva  of  a  coleoptera  within  the  fasciated 
stems  of  Raphamis  raphanistruni  and  of  Picris  hieracioides ,  just  below  the 
banded  portions  of  the  axis.  He  suggested  that  the  parasite  modified  the 
structure  of  the  vegetative  point  and  changed  the  mass  of  the  initial  mer- 
istem from  axial  symmetry  to  the  symmetry  of  a  line. 

Peyritsch  (5),  in  his  interesting  experiments  on  the  production  of  abnor- 
malities through  inoculation  with  Phytopiis,  enumerates,  among  the  aberrant 


16         INDUCTION,   DEVELOPMENT,   AND  HERITABILITY  OF  FASCIATIONS. 

forms  found  in  the  Valerianaceae ,  "fasciation  of  side-branches  of  a  slii^ht 
degree  and  disarrangement  of  phyllotaxy."  He  later  says:  "All  the 
foregoing  anomalies  are  phenomena  of  infection  and  owe  their  form  to  the 
stimulus  of  a  parasite. ' '  Althougrh  these  experiments  were  never  published 
in  detail,  and  emphasis  was  laid  on  phenomena  other  than  those  of  fascia- 
tion, the  hypothesis  that  fasciation  was  due  to  infection  was  evidently  in 
the  author's  mind.  Had  he  lived  longer  he  might  have  taken  u])  the  sub- 
ject more  specifically  and  demonstrated  it  in  relation  to  the  Valerianaceae. 
He  concludes  his  article  with  the  following  sentence:  "I  am  convinced 
that  many  instances  which  have  hitherto  been  explained  as  spontaneous 
variations  owe  their  origin  to  the  activity  of  insects,  although  a  Phytopus 
need  not  always  be  the  stimulus." 

The  analogy  of  the  artificial  production  of  fasciation  leads  one  to  infer 
that  the  insect  is  but  very  indirectly  the  cause,  and  that  the  physiology  is 
the  physiology  of  traumatic  after-effects.  The  nature  of  the  changes  in  the 
chemical  and  physical  conditions  of  cells  after  wounding  is  as  yet  but  im- 
perfectly understood,  and  the  enormous  hyperplasies  resulting  from  the 
mechanical  irritation  of  foreign  substances,  especially  those  associated  with 
the  parasitism  of  insects,  are  among  the  most  interesting  of  unexplained 
physiological  phenomena. 

The  following  points  are  to  be  emphasized  in  summing  up  the  foregoing 
statements: 

(1)  In  the  Oenotheras  the  histology  of  the  early  stages  of  development  of 
fasciated  stems  is  varied.  Many  different  forms  are  found  related  anatom- 
ically to  each  other  and  to  ring-fasciations .  All  may  occur  on  the  same  plant , 
and  the  differences  between  them  are  morphological,  not  physiological. 

(2)  The  fasciations  arise  through  the  agency  of  injuries  inflicted  upon 
the  growing  regions  by  insects.  Bifurcations  without  definite  flattening 
develop  through  the  same  set  of  stimuli. 

(3)  The  injuries  must  be  inflicted  upon  the  initial  meristem,  and  can 
ordinarily  be  detected  only  microscopically,  and  at  the  earliest  period  of  the 
ensuing  growth.  In  such  cases  their  course  is  almost  immediately  obscured 
or  obliterated  by  the  development  of  the  surrounding  cells. 

(4)  Injuries  may  result  in  the  abortion  of  the  whole  or  part  of  an  axis, 
or  in  the  formation  of  small  processes  on  the  stem.  These  malformations 
are  described  as  "protuberances,"  and  their  development  is  almost  invar- 
iably associated  with  fasciation  or  bifurcation,  or  both. 

(5)  Plants  infected  early  in  the  rosette  stage  fasciate  as  rosettes;  those 
infected  after  the  stems  have  begun  to  elongate  are  fasciated  only  in  the 
upper  parts  of  the  branches. 

(6)  To  secure  the  greatest  number  of  fasciations,  the  plants  should  be 
given  the  best  conditions  for  their  individual  development,  and  the  seed 
should  be  planted  so  that  the  period  of  greatest  vigor  may  correspond  with 
the  time  when  they  are  most  sure  of  infection. 


INDUCTION,   DEVELOPMENT,   AND  HERITABILITY  OF  FASCIATIONS.  17 

(7)  The  morphology  of  the  fasciated  stem  is  the  enlarg-ement  of  a  single 
gfrowing-  point.     There  is  no  evidence  of  fusion  in  the  growing-  region. 

(8)  When  tested  in  pure  cultures,  the  progeny  of  fasciated  individuals 
show  no  greater  tendenc\-  to  fasciation  than  the  progeny  of  normal  plants. 
The  effects  of  the  stimuli  causing  these  malformations  in  the  evening-prim- 
rose are  therefore  to  be  taken  as  in  no  wise  heritable. 

In  conclusion,  the  writer  wishes  to  express  her  appreciation  of  the  assis- 
tance and  of  the  many  courtesies  extended  to  her  by  Dr.  D.  T.  MacDougal, 
Dr.  H.  M.  Richards,  and  by  the  director  and  the  members  of  the  staff  of 
the  New  York  Botanical  Garden.  The  work  was  begim  imder  the  auspices 
of  the  garden  and  continued  under  those  of  the  Carnegie  Institution  of 
Washington. 


LITERATURE  CITED. 

1.  Knight.     On  the  cultivation  of  the  cockscomb.     Trans.  Hort.  Soc.  of   London, 

4 ; 321,  1820. 

2.  Mouquin-Tandon,  a.     Elements  de  teratologie  vcgetale.     Paris,  1S41. 

3.  Masters,  M.  T.     Vegetable  teratology.     London,  1869. 

4.  GoDRON.     Melanges  teratologiques.     Mem.  de  la  Soc.  nat.  dessc.  nat.  de  Cherbourg, 

16:  1871-72.  .. 

5.  Peyritsch,  J.      iJber  kiinstliche  Erzeugung  von   gefiillten  Bliithen  und  anderen 

Bildungsabweichungen.     Sitzber.  d.  k.  Akad.  d.  Wiss.  in  Wien,  math.-naturw., 
CI.,  97:597,  18SS. 

6.  Sachs,  J.     Gesammelte  Abhandlungen  iiber  Pflanzen-Physiologie,  1  :  597,  1892. 

7.  Nestler,  A.     Untersuchungen  iiber  Fasciationen.     Oesterr.  bot.  Zeitschr.,  44  :  543, 

'894- 

8.  Nestler,  A.     Uber  ring  fasciation.     Sitzber.  d.   k.   Akad.  d.  wiss.  Wien,  math.- 

naturw.  CI.,  103:  153,  1894. 

9.  De  Vries,  H.      Over  de   Erfelijkheid  der  Fasciatien.      Bot.  Jaarboek  Dodonaea, 

6:  72,  1S94. 

10.  Ramaley,  F.     On  the  stem  anatomy  of  certain  Onagraceas.     Minn.  Bot.  Studies, 

1  : 674,  1896. 

11.  De  Vries,  H.     Sur  la  culture  des  fasciations  des  especes  annuelles  et  biannuelles. 

Rev.  gen.  de  bot.,  1 1  :  136,  1899. 

12.  De  Vries,  H.     Sur  la  culture  des  monstruosites.    Comptes  Rendus,  Paris,  128  :  125, 

1899. 

13.  De  Vr  ies,  H.     Uber  die  Abhangigkeit  der  Fasciation  vom  Alter  bei  zweijahriger 

Pflanzen.     Bot.  Centralblatt,  77  :  289,  1S99 

14.  La.makliere,  G.  de.     Sur  la  production  experimentale  des  tiges  et  d'inflorescences 

fascides.     Comptes  Rendus,  Paris,  128  :  1601,  1899. 

15.  Molliard,  M.     Cas  de  virescence  et  de  fasciation  d'origine  parisitaire.     Rev.  gen. 

de  bot.,  12  :  323,  1900. 

16.  GoEBEL,  K.     Organography  of  plants.     Part  I.     Oxford,  1900. 

17.  Renaudet,  G.     Contribution  k  I'dtude  de  la  tdratologie  vegetale  de  la  fasciation 

herbacde  et  ligneuse.     These,  Poitiers,  1901. 

18.  CoNARD,  H.  S.     Fasciation  in  the  sweet  potato.     Univ.  of  Penn  ,  Bot.  Lab.  Contrib., 

2 : 205,  1901. 

19.  De  Vries,  H.     Die  Mutations-Theorie.     Leipzig,  1901. 

20.  De  Vries,  H.     Species  and  varieties.     Chicago,  1905. 

21.  Blodgett,  F.  H.     Fasciation  in  field  peas.     Plant  World,  8  :  170,  1905. 

22.  Hus,  H.     Fasciation  in   Oxalis  creiiata  and  experimental  production  of  fasciation. 

Rept.  Missouri  Bot.  Gard.,  17:  147,  1906. 

23.  PuGLiSL   M.      Contributo  alia  teratologia  vegetale.      i.    Fasciazione    di    Vescaria 

reticula,  di  Bunias  orientalis.    Ann.  di  botanica,  4  :  367,  1906. 


18         INDUCTION,    DEVELOPMENT,   AND  PIERITABILITY  OF  FASCIATIONS. 


Desckii'tion  of  Plate  IV. 

Sciiii-diagratninaiic  transverse  sections  of  stet/is;  size  reduced  to  tivo-scvenths  of  given 

magnifications. 

Series  i.  O.  biennis.  Successive  stages  in  the  development  of  a  groove-fasciation 
Medullary  parenchyma,  mp;  region  of  cambium,  c;  region  of  outer  phloem  and 
stereome  ring,^//,/  region  of  the  inner  phloem, ///j/  xylem,  .ij/ cortex,  ^ta/ 
epidermis,  ep.     X  44. 

a.  Initial  appearance  of  meristem,^^. 

/;.  Appearance  of  supplementary  meristems,  Wj,w^, ;  position  of  groove,^;  thick- 
walled  parenchyma  surrounding  meristems,//. 

c.  Differentiation  of  secondary  bundles,  b^  ,  b.^,  b-^,  etc.:  callus,  cl. 

d.  Gradual  enlargement  and  increase  of  secondary  bundles;  region  of  outer  phloem 

and  of  stereome  ring,///.,  ;  region  of  inner  phloem,/^//,,-  xylem,.r)'., /cambium,  (.,. 

e.  Union  of  secondary  bundles  with  primary  ring. 

f  Last  stage  before  complete  fusion  with  primary  ring. 
Series  2.  O.  crticiata.     Development  of  a  fasciation  associated  with  a  cylindrical  pro- 
tuberance.    Lettering  as  before.     X  18. 

a.  Initial  appearance  of  meristem,  ni. 

b.  Differentiation  of  secondary  bundle-ring,  b^,.,  in  the  pith. 

c.  Connection  of  secondary  bundle-ring  with  the  primary  ring. 

d.  Fusion  of  the  same. 

e.  Beginning  of  formation  of  protuberance  at  k. 

f.  Protuberance  cut  off,  /'. 

Series  3.  O.  biennis.     Development  of  ring-fasciation.     X  25. 

a.  Appearance  of  a  single  meristem,  in. 

b.  Development  of  supplementary  meristems,  //Zj,  ;«., ,  ;//;,,  etc. 

c.  Differentiation  of  meristems  into  ring  of  secondary  bundle-groups,  b-^  ,  b., ,  A,,  etc. 

d.  Appearance  of  lysigenous  cavity,  ca. 

e.  Gradual  fusion  of  secondary  bundle-groups.     Inner  epidermis,  ep.,;  inner  cortex, 

cx<.:  outer  phloem  of  secondary  ring,  ph-^;  inner  phloem  of  secondary  ring, 
///,,•  xvlem,;ij._,;  pith,//. 
/.  Break  in  side  of  ring,  making  a  flat  fasciation. 
Series  4.  O.  biennis.  Four  stages  of  the  development  of  a  specimen  intermediate 
between  Series  i  and  3.  i\a  corresponds  with  y.  The  secondary  bundle-ring 
arises  in  the  middle  and  passes  to  the  side,  where  it  fuses  with  the  primary 
ring.     X  20. 


Knox. 


Plate  IV. 


20         INDUCTION,   DEVELOPMENT,   AND  HERITABILITY  OF  FASCIATIONS. 


Description  of  Plate  V. 

[Drawn  with  an  Abbe  catueru  lucida  and  reduced  to  one-third  of  given  magnifications.  I 

Figs  i,  2,  3.  Transverse  sections  of  stems  of  O.  biennis.  Successive  stages  in  the  early 
development  of  a  groove-fasciation.  Meristem,  ;//,•  thick-walled  parenchyma, 
pp;  medullary  parenchyma,  ;;/^;  cambium,  c;  outer  phloem  of  primary  bundle 
ring,/"//, ;  inner  phloem  of  same  ring,  ^Z/^.  Fig.  i  shows  the  lowest  section  of 
the  meristem  (plate  iv,  fig.  \a).  The  dark  shading  in  the  meristem  indicates 
intercellular  secretions.     At  .r  the  cambium  has  been  destroyed.     X  430. 

Fig.  2.  Drawing  of  meristems  in  plate  iv,  fig.  \b.  Two  meristems  {>n-^,/;i..)  appear  in  the 
break  in  the  ring.     X  430. 

Fig.  3.  Drawing  of  two  groups  of  secondary  bundles,  showing  first  differentiation  of 
vessels.     Secondary  bundle-groups,  b^ ,  b...     X  560. 

Fig.  4.  O.  cniciata.  Diagram  of  longitudinal  section  of  a  cylindrical  protuberance. 
Bundle-ring,  b;  callus,  cl;  cortex,  ex.     X  25. 

Fig.  5.  O.  cruciata     The  same  as  fig.  4-     Group  of  callus  cells  from  the  apex.     X  360. 

Fig.  6.  O.  cruciata.  The  same  as  figs.  4  and  5.  Drawing  of  portion  of  apex  of  bundle- 
ring  opposite  point  marked  z  in  fig.  4.  Spiral  ducts  run  transversely  across 
the  tip. 

Fig.  7.  O.  cruciata.  Diagram  of  longitudinal  section  of  apex  of  plant  shown  in  fig.  8. 
Sections  of  vegetative  circle,  vc;  callus,  cl;  primary  bundle  ring,  b.     X  iS^. 

Fig.  8.  O.  cruciata.  Longitudinal  section  of  apex  of  fig.  7  at  cl.  Callus,  cl;  proto- 
^h\o&m,  ph^,  ph.,;  proto-xylem  showing  spiral  ducts,  xy.  This  is  an  early 
stage  in  the  formation  of  a  protuberance.     X  360. 

Fig.  9.  O.  cruciata.  Diagram  of  cross-section  of  base  of  fasciated  rosette  which  shows 
traces  of  injury.  The  oval  shape  of  the  pith  shows  the  beginning  of  the 
flattening.  Phellogen,  pg;  bark,  bk;  meristems  in  pith,  ww/  callus  at  point  of 
inhibition  of  growth,  cl.      X  8. 

Fig.  10.  O.  cruciata.  Diagram  of  longitudinal  section  of  bifurcated  tip,  showing  posi- 
tion of  callus,  cl.  At  q  the  bundle-elements  run  irregularly  in  a  confused 
tangle.     K  is  a  small  protuberance.     X  52. 

Fig.  II.  O.  cruciata.  Drawing  of  longitudinal  section  of  apex  similar  to  fig.  13.  An 
incision  surrounded  by  hypertrophy  and  meristematic  divisions.  The  con- 
tents of  the  cavity  are  stained  reddish  purple.     X  560. 

Fig.  12.  O.  cruciata.  The  same  as  fig.  11.  Cells  in  pith  surrounding  the  lower  end  of 
incision.  The  blackened  edges  indicate  purplish  discoloration  between  the 
cells.  The  cells  hypertrophy  and  close  in  around  the  incision  without  dividing. 
X  480. 

Fig.  13.  O.  cruciata.  Diagrammatic  longitudinal  section  of  an  injured  tip  similar  to  the 
one  pictured  in  figs.  1 1  and  12.  The  apex  seems  to  be  slightly  fasciated,  and 
the  stem  is  bifurcated,     z,  injury.     X  25. 

Fig.  14.  O.  cruciata.  Transverse  section  of  early  stage  of  ring-fasciation.  The  inter- 
cellular conditions  indicate  that  it  has  been  injured.  Cf.  fig.  12.  w,  two  cells 
of  the  meristem.     X  560. 

Fig.  15.  O.  cruciata.  Transverse  sections  of  ring-fasciation  in  fig.  14  at  a  more  advanced 
stage.  Secondary  bundle-ring,  b.,.  In  the  center  of  the  pith  is  a  cavity  sur- 
rounded by  hypertrophied  cells  and  meristematic  divisions.  This  is  not  the 
beginning  of  the  lysigenous  cavity  of  the  ring,  which  occurs  some  sections 
above.     X  430. 

Fig.  16.  Transverse  section  of  flowering  stem  just  below  the  point  of  fasciation,  showing 
inhibition  in  the  formation  of  wood  at  xx.     X  25. 

Fig.  17.  Raimannia  odorata.  Cross-section  of  young  bifuricated  rosette,  showing  injury 
to  cortex  and  inhibition  in  the  development  of  the  bundle-ring  at  xx.     X  92. 


Knox. 


Plate  V. 


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DN  DEVELOPMENT 

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SdScT,On\eVELOPMENT  and  HERITABILITY  OF  FAS 


